Andrei G Lebed

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Books

• Lebed, A. G. (2008). The Physics of Organic Superconductors and Conductors. Springer (Berlin, Heidelberg, New York).

Journals/Publications

• Lebed, A. G. (2020). Breakdown of the Einstein’s Equivalence Principle for a quantum body. Modern Physics Letters A, 35(20), 2030010.
• Lebed, A. G. (2020). Four-fold anisotropy of the parallel upper critical magnetic field in a pure layered d-wave superconductor at T = 0. JETP Letters, 111(4), 239.
• Lebed, A. G. (2020). Restoration of superconductivity in high magnetic fields in UTe2. Modern Physics Letters B, 34(32), 2030007.
• Lebed, A. G. (2019). Breakdown of the equivalence between gravitational mass and energy due to quantum effects. International Journal of Modern Physics D, 28(12), 1930020-1 - 1930020-22.
• Lebed, A. G. (2019). Layered superconductor in a magnetic field: breakdown of the effective masses model. JETP Letters, 110(3), 173-177.
• Lebed, A. G. (2019). Unconventional field-induced spin density wave phases in quasi-one-dimensional conductors in high magnetic fields. Physical Review B (Rapid Communication), 99, 041103(R)-1 - 041103(R)-5.
• Lebed, A. G. (2018). Destruction of the spin-density-wave phase by magnetic field in a quasi-one-dimensional conductor. Physical Review B (Rapid Communications), 97, 220503(R).
• Lebed, A. G. (2017). Inequivalence between gravitational mass and energy due to quantum effects at microscopic and macroscopic levels. International Journal of Modern Physics D, 26, 1730022.
• Lebed, A. G. (2017). Quantum limit in a quasi-one-dimensional conductor in a high tilted magnetic field. JETP Letters, 106, 509-513.
• Lebed, A. G. (2017). Response to: Comment on “Does the Equivalence between Gravitational Mass and Energy Survive for a Composite Quantum Body?”. Advances in High Energy Physics, 2017, 1683075.
• Lebed, A. G. (2016). Breakdown of the equivalence between active gravitational mass and energy for a quantum body. Journal of Physics: Conference Series, 738, 012036.
• Lebed, A. G. (2016). Non-Fermi-liquid magic angle effects in high magnetic fields. Physical Review B, 94, 035162.
• Lebed, A. G. (2016). Possible existence of superconductivity in the quasi-one-dimensional conductor Li0.9Mo6O17 at ultrahigh magnetic fields (H ≥ 45 T). Physical Review B, 93, 094523.
• Lebed, A. G. (2015). Breakdown of the equivalence between gravitational mass and energy for a quantum body: Theory and suggested experiments. International Journal of Modern Physics D, 24, 1530027-1 - 1530027-23.
• Lebed, A. G. (2015). Non-Fermi-Liquid Crossovers in a Quasi-One-Dimensional Conductor in a Tilted Magnetic Field. Physical Review Letters, 115, 157001-1 - 157001-5.
• Lebed, A. G., & Sepper, O. (2015). Quantum limit and reentrant superconducting phases in the Q1D conductor Li(0.9)Mo(6)O(17). Physica B, 460, 231-235.
• Lebed, A. G. (2014). Breakdown of the equivalence between gravitational mass and energy for a composite quantum body. Journal of Physics: Conference Series, 490(1).
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  Abstract: The simplest quantum composite body, a hydrogen atom, is considered in the presence of a weak external gravitational field. We define an operator for the passive gravitational mass of the atom in the post-Newtonian approximation of the general relativity and show that it does not commute with its energy operator. Nevertheless, the equivalence between the expectation values of the mass and energy is shown to survive at a macroscopic level for stationary quantum states. Breakdown of the equivalence between passive gravitational mass and energy at a microscopic level for stationary quantum states can be experimentally detected by studying unusual electromagnetic radiation, emitted by the atoms, supported by and moving in the Earth's gravitational field with constant velocity, using spacecraft or satellite. © Published under licence by IOP Publishing Ltd.
• Lebed, A. G. (2014). Does the equivalence between gravitational mass and energy survive for a composite quantum body?. Advances in High Energy Physics, 2014.
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  Abstract: We define passive and active gravitational mass operators of the simplest composite quantum body - a hydrogen atom. Although they do not commute with its energy operator, the equivalence between the expectation values of passive and active gravitational masses and energy is shown to survive for stationary quantum states. In our calculations of passive gravitational mass operator, we take into account not only kinetic and Coulomb potential energies but also the so-called relativistic corrections to electron motion in a hydrogen atom. Inequivalence between passive and active gravitational masses and energy at a macroscopic level is demonstrated to reveal itself as time-dependent oscillations of the expectation values of the gravitational masses for superpositions of stationary quantum states. Breakdown of the equivalence between passive gravitational mass and energy at a microscopic level reveals itself as unusual electromagnetic radiation, emitted by macroscopic ensemble of hydrogen atoms, moved by small spacecraft with constant velocity in the Earth's gravitational field. We suggest the corresponding experiment on the Earth's orbit to detect this radiation, which would be the first direct experiment where quantum effects in general relativity are observed. © 2014 A. G. Lebed.
• Lebed, A. G., & Sepper, O. (2014). Possible restoration of superconductivity in the quasi-one-dimensional conductor Li0.9Mo6O17 in pulsed high magnetic fields H = 100 T. Physical Review B, 90, 094509.
• Lebed, A. G., & Sepper, O. (2014). Quantum limit in a magnetic field for triplet superconductivity in a quasi-one-dimensional conductor. Physical Review B.
• Lebed, A. G. (2013). Is gravitational mass of a composite quantum body equivalent to its energy?. Central European Journal of Physics, 11(8), 969-976.
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  Abstract: We define passive gravitational mass operator of a hydrogen atom in the post-Newtonian approximation of general relativity and show that it does not commute with energy operator, taken in the absence of gravitational field. Nevertheless, the equivalence between the expectation values of passive gravitational mass and energy is shown to survive for stationary quantum states. Inequivalence between passive gravitational mass and energy at a macroscopic level results in time dependent oscillations of the expectation values of passive gravitational mass for superpositions of stationary quantum states, where the equivalence restores after averaging over time. Inequivalence between gravitational mass and energy at a microscopic level reveals itself as unusual electromagnetic radiation, emitted by the atoms, supported and moved in the Earth gravitational field with constant velocity using spacecraft or satellite, which can be experimentally measured. © 2013 Versita Warsaw and Springer-Verlag Wien.
• Lebed, A. G., & Sepper, O. (2013). Possible triplet superconductivity in the quasi-one-dimensional conductor Li_0.9Mo₆O₁₇. Physical Review B - Condensed Matter and Materials Physics, 87(10).
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  Abstract: We consider a theoretical problem of the upper critical magnetic field parallel to a conducting axis of a quasi-one-dimensional layered superconductor. We show that the orbital effects against superconductivity in a magnetic field are capable of destroying the superconducting phase at low temperatures if the interplane distance is less than the corresponding coherence length. Applications of our results to recent experiments, performed in the superconductor Li0.9Mo6O17, provide strong arguments in favor of a triplet superconducting pairing in this quasi-one-dimensional layered conductor. © 2013 American Physical Society.
• Sepper, O., & Lebed, A. G. (2013). Nodeless versus nodal scenarios of possible triplet superconductivity in the quasi-one-dimensional layered conductor Li_0.9Mo₆O ₁₇. Physical Review B - Condensed Matter and Materials Physics, 88(9).
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  Abstract: We consider the problem of the orbital upper critical magnetic field, parallel to the most conducting axis of a quasi-one-dimensional layered superconductor. It is shown that superconductivity can be destroyed through orbital effects at fields much higher than the so-called Clogston-Chandrasekhar paramagnetic limiting field Hp, provided that superconducting pairing of electrons are of a triplet nature. We demonstrate that the superconducting state of the quasi-one-dimensional layered conductor Li0.9Mo 6O17 is well described by the suggested theory. To this end, we consider two competing scenarios: (1) a superconducting order parameter without zeros on the Fermi surface, and (2) one with zeros on the Fermi surface - both are shown to lead to destruction of superconductivity at a magnetic field Hc2x, five times higher than Hp. With recent experimental measurements on the Li0.9Mo6O17 favoring the nodeless order parameter, we present a strong argument supporting triplet pairing in this compound. © 2013 American Physical Society.
• Lebed, A. G. (2012). D-Wave-like nodal superconductivity in the organic conductor (TMTSF) ₂ClO ₄. Physica B: Condensed Matter, 407(11), 1803-1805.
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  Abstract: We suggest theoretical explanation of the high upper critical magnetic field, perpendicular to conducting chains, Hc2 b′, experimentally observed in the superconductor (TMTSF) 2ClO 4, in terms of singlet superconducting pairing. In particular, we compare the results of d-wave-like nodal, d-wave-like node-less, and s-wave scenarios of superconductivity. We show that, in d-wave-like nodal scenario, superconductivity can naturally exceed both the orbital upper critical magnetic field and Clogston-Shandrasekhar paramagnetic limit as well as reach experimental value, Hc2 b′≃6T, in contrast to d-wave-like node-less and s-wave scenarios. In our opinion, the obtained results are strongly in favor of d-wave-like nodal superconductivity in (TMTSF) 2ClO 4, whereas, in a sister compound, (TMTSF) 2PF 6, we expect either the existence of triplet order parameter or the coexistence of triplet and singlet order parameters. © 2012 Elsevier B.V. All rights reserved.
• Lebed, A. G. (2012). Ginzburg-Landau slopes of the anisotropic upper critical magnetic field and band parameters in the superconductor (TMTSF) ₂ClO ₄. JETP Letters, 94(9), 689-692.
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  Abstract: We theoretically determine the Ginzburg-Landau slopes of the anisotropic upper critical magnetic field in a quasi-one-dimensional superconductor and correct the previous works on this issue. By using the experimentally measured values of the Ginzburg-Landau slopes in the superconductor (TMTSF)ClO 4, we determine band parameters of its electron spectrum. Our main result is that the so-called quantum dimensional crossover has to happen in this material in magnetic fields, H = 3-8 T, which are much lower than the previously assumed. We discuss how this fact influences metallic and superconducting properties of the (TMTSF) 2ClO 4. © 2011 Pleiades Publishing, Ltd.
• Lebed, A. G., & Sepper, O. (2012). Non-analytical angular dependence of the upper critical magnetic field in a quasi-one-dimensional superconductor. JETP Letters, 96(3), 176-180.
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  Abstract: We have derived the so-called gap equation, which determines the upper critical magnetic field, perpendicular to conducting chains of a quasi-one-dimensional superconductor. By analyzing this equation at low temperatures, we have found that the calculated angular dependence of the upper critical magnetic field is qualitatively different than that in the so-called effective mass model. In particular, our theory predicts a non-analytical angular dependence of the upper critical magnetic field, H c2(0) - H c2(α) ~ α 3/2, when magnetic field is close to some special crystallographic axis and makes an angle α with it. We discuss possible experiments on the superconductor (DMET) 2I 3 to discover this non-analytical dependence. © 2012 Pleiades Publishing, Ltd.
• Lebed, A. G. (2011). Ginzburg-Landau Slopes of the Anisotropic Upper Critical Magnetic Fields and Band Parameters in the Superconductor (TMTSF)2ClO4. JETP Letters.
• Lebed, A. G. (2011). Hidden reentrant and Larkin-Ovchinnikov-Fulde-Ferrell superconducting phases in a magnetic field in a (TMTSF)₂ClO₄. Physical Review Letters, 107(8).
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  Abstract: We solve a long-standing problem about a theoretical description of the upper critical magnetic field, parallel to conducting layers and perpendicular to conducting chains, in a (TMTSF)2ClO4 superconductor. In particular, we explain why the experimental upper critical field, Hc2b ′6T, is higher than both the quasiclassical upper critical field and the Clogston paramagnetic limit. We show that this property is due to the coexistence of the hidden reentrant and Larkin-Ovchinnikov-Fulde-Ferrell phases in a magnetic field in the form of three plane waves with nonzero momenta of the Cooper pairs. Our results are in good qualitative and quantitative agreement with the recent experimental measurements of Hc2b′ and support a singlet d-wave-like scenario of superconductivity in (TMTSF) 2ClO4. © 2011 American Physical Society.
• Lebed, A. G. (2011). Hidden reentrant superconducting phase in a magnetic field in (TMTSF)₂ClO₄. JETP Letters, 94(5), 382-385.
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  Abstract: We suggest explanation of the high upper critical magnetic field, perpendicular to conducting chains and parallel to conducting layers Hc2b'≃ 6 T, experimentally observed in the organic superconductor (TMTSF)2ClO4. In particular, we show that Hc2b' can be higher than both the quasiclassical upper critical field and Clogston-Chandrasekhar paramagnetic limit in a singlet quasi-one-dimensional superconductor. We predict the coexistence of the hidden Reentrant and Larkin-Ovchinnikov-Fulde-Ferrell phases in a magnetic field. Our results are compared to the recent experimental data and shown to be in a good agreement with the experiments. © 2011 Pleiades Publishing, Ltd.
• Lebed, A. G. (2010). Universal field-induced spin-density-wave phases: Theory versus experiment. Physica B: Condensed Matter, 405(11 SUPPL.), S106-S107.
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  Abstract: We suggest a universal theory of the field-induced spin-density-wave phase diagrams, experimentally observed in (TMTSF) 2X conductors. In particular, we show that, in layered quasi-one-dimensional conductors, the critical magnetic fields ratios, H 1/H 0 = 0.73, H 2/H 0 = 0.59, and H 3/H 0 =0.49, are universal and do not depend on any fitting parameter. The suggested theory is in a good qualitative and quantitative agreement with the existing experimental data. © 2010 Elsevier B.V. All rights reserved.
• Lebed, A. G., & Si, W. u. (2010). Larkin-Ovchinnikov-Fulde-Ferrell phase in the superconductor (TMTSF) ₂ ClO₄: Theory versus experiment. Physical Review B - Condensed Matter and Materials Physics, 82(17).
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  Abstract: We consider a formation of the Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase in a quasi-one-dimensional (Q1D) conductor in a magnetic field, parallel to its conducting chains, where we take into account both the paramagnetic spin splitting and orbital destructive effects against superconductivity. We show that, due to a relative weakness of the orbital effects in a Q1D case, the LOFF phase appears in (TMTSF)2 ClO4 superconductor for real values of its Q1D band parameters. We compare our theoretical calculations with the recent experimental data by Y. Maeno's group and show that there is a good qualitative and quantitative agreement between the theory and experimental data. © 2010 The American Physical Society.
• Si, W. u., & Lebed, A. G. (2010). Unification theory of angular magnetoresistance oscillations in quasi-one-dimensional conductors. Physical Review B - Condensed Matter and Materials Physics, 82(7).
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  Abstract: We present a unification theory of angular magnetoresistance oscillations, experimentally observed in quasi-one-dimensional organic conductors, by solving the Boltzmann kinetic equation in the extended Brillouin zone. We find that, at commensurate directions of a magnetic field, resistivity exhibits strong minima. In two limiting cases, our general solution reduces to the results, previously obtained for the Lebed Magic Angles and Lee-Naughton-Lebed oscillations. We demonstrate that our theoretical results are in good qualitative and quantitative agreement with the existing measurements of resistivity in (TMTSF) 2 ClO4 conductor. © 2010 The American Physical Society.
• Lebed, A. G. (2009). Universal Field-Induced Charge-Density-Wave Phase Diagram: Theory versus Experiment. Physical Review Letters, 103(4).
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  Abstract: We suggest a theory of field-induced charge-density-wave phases, generated by high magnetic fields in quasi-low-dimensional conductors. We demonstrate that, in layered quasi-one-dimensional conductors, the corresponding critical magnetic field ratios are universal and do not depend on any fitting parameter. In particular, we find that H1/H0=0.73, H2/H0=0.59, H3/H0=0.49, and H4/H0=0.42, where Hn is a critical field of a phase transition between the field-induced charge-density-wave phases with numbers n and n+1. The suggested theory is in very good qualitative and quantitative agreement with the existing experimental data in α-(ET)2KHg(SCN)4 material. © 2009 The American Physical Society.
• Lebed, A. G., & Wu, S. (2009). Super-crystalline phase in quasi-one-dimensional conductors. Physica B: Condensed Matter, 404(3-4), 347-349.
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  Abstract: A model, where phase transition between the Peierls and periodic soliton wall superlattice (super-crystalline) charge-density-wave phases occur in a magnetic field, is proposed. The model accounts for the peculiarities of the phase diagram in a quasi-one-dimensional conductor (Per)2Pt(mnt)2. In the absence of a magnetic field, our model is equivalent to the exactly solvable model of Brazovskii, Dzyaloshinskii, and Kirova. © 2008 Elsevier B.V. All rights reserved.
• Si, W. u., & Lebed, A. G. (2009). Soliton wall superlattice charge-density-wave phase in the quasi-one-dimensional conductor (Per) 2 Pt (mnt) 2. Physical Review B - Condensed Matter and Materials Physics, 80(3).
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  Abstract: We demonstrate that the Pauli spin-splitting effects in a magnetic field improve nesting properties of a realistic quasi-one-dimensional electron spectrum. As a result, a high resistance Peierls charge-density-wave (CDW) phase is stabilized in high enough magnetic fields in (Per) 2 Pt (mnt) 2 conductor. We show that, in low and very high magnetic fields, the Pauli spin-splitting effects lead to a stabilization of a soliton wall superlattice (SWS) CDW phase, which is characterized by periodically arranged soliton and antisoliton walls. We suggest experimental studies of the predicted first-order phase transitions between the Peierls and SWS phases to discover a unique SWS phase. It is important that, in the absence of a magnetic field and in a limit of very high magnetic fields, the suggested model is equivalent to the exactly solvable model of Brazovskii, Dzyaloshinskii, and Kirova for the Su-Schrieffer-Heeger solitons. © 2009 The American Physical Society.
• Dutta, O., & Lebed, A. G. (2008). Cooper pairs with broken time-reversal, parity, and spin-rotational symmetries in singlet type-II superconductors. Physical Review B - Condensed Matter and Materials Physics, 78(22).
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  Abstract: We show that singlet superconductivity in the Abrikosov vortex phase is absolutely unstable with respect to the appearance of a chiral triplet component of a superconducting order parameter. This chiral component p x+ipy breaks time-reversal, parity, and spin-rotational symmetries of the internal order parameter responsible for a relative motion of two electrons in the Cooper pair. We demonstrate that the symmetry-breaking Pauli paramagnetic effects can be tuned by a magnetic-field strength and direction and can be made of the order of unity in organic and high-temperature layered superconductors. © 2008 The American Physical Society.
• Lebed, A. G. (2008). Paramagnetic intrinsic Meissner effect in a bulk. JETP Letters, 88(3), 201-204.
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  Abstract: We calculate the free energy of a quasi-two-dimensional (Q2D) superconductor with ξ⊥ < d in a parallel magnetic field, where ξ⊥ is a perpendicular to the conducting layer coherence length and d is the interlayer distance. It is shown to be different from that in the famous Lawrence-Doniach model. In particular, at high enough magnetic fields, the Meissner currents are found to create an unexpected paramagnetic moment due to the shrinking of the Cooper pairs "sizes" in a direction perpendicular to the conducting layers. We suggest measuring this paramagnetic intrinsic Meissner effect in Q2D superconductors and superconducting superlattices. © 2008 Pleiades Publishing, Ltd.
• Lebed, A. G. (2008). Paramagnetic intrinsic Meissner effect in layered superconductors. Physical Review B - Condensed Matter and Materials Physics, 78(1).
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  Abstract: Free energy of a layered superconductor with ξ
• Lebed, A. G., & Si, W. u. (2007). Soliton wall superlattice in the quasi-one-dimensional conductor (Per)2Pt(mnt)2. Physical Review Letters, 99(2).
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  Abstract: We suggest a model to explain the appearance of a high resistance high magnetic field charge-density-wave (CDW) phase, discovered by Graf et al. in (Per)2Pt(mnt)2, where Per is perylene and mnt is maleonitriledithiolate molecules. In particular, we show that the Pauli spin-splitting effects improve the nesting properties of a realistic quasi-one-dimensional electron spectrum and, therefore, a high resistance Peierls CDW phase is stabilized in high magnetic fields. In low and very high magnetic fields, a periodic soliton wall superlattice (SWS) phase is found to be a ground state. We suggest experimental studies of the predicted phase transitions between the Peierls and SWS CDW phases in (Per)2Pt(mnt)2 to discover a unique SWS phase. © 2007 The American Physical Society.
• Lebed, A. G., & Wu, S. (2007). Soliton wall superlattice charge-density-wave phase in a magnetic field. JETP Letters, 86(2), 135-138.
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  Abstract: A model where phase transitions between the Peierls and periodic soliton wall superlattice (SWS) charge-density-wave phases occur in a magnetic field is proposed. The model accounts for the peculiarities of the electron spectrum in a quasi-one-dimensional conductor (Per)2Pt(mnt)2. Possible experimental investigations of the theoretically predicted phase transitions in (Per)2Pt(mnt)2 to discover a unique SWS phase are discussed. © 2007 Pleiades Publishing, Ltd.
• Ha, H. I., Lebed, A. G., & Naughton, M. J. (2006). Interference effects due to commensurate electron trajectories and topological crossovers in (TMTSF) 2 ClO4. Physical Review B - Condensed Matter and Materials Physics, 73(3).
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  Abstract: We report angle-dependent magnetoresistance measurements on (TMTSF) 2 ClO4 that provide strong support for a macroscopic quantum phenomenon, the "interference commensurate" (IC) effect, in quasi-one dimensional metals. In addition to observing rich magnetoresistance oscillations, and fitting them with one-electron calculations, we observe a clear demarcation of field-dependent behavior at local resistance minima and maxima (versus field angle). Anticipated by a theoretical treatment of the IC effect in terms of Bragg reflections in the extended Brillouin zone, this behavior results from one-dimensional → two dimensional (1D→2D) topological crossovers of electron wave functions as a function of field orientation. © 2006 The American Physical Society.
• Lebed, A. G. (2006). Cooper pairs with broken parity and spin-rotational symmetries in d-wave superconductors. Physical Review Letters, 96(3).
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  Abstract: Paramagnetic effects are shown to result in the appearance of a triplet component of order parameter in a vortex phase of a d-wave superconductor in the absence of impurities. This component, which breaks parity and spin-rotational symmetries of Cooper pairs, is expected to be of the order of unity in a number of modern superconductors such as organic, high Tc, and some others. A generic phase diagram of such type-IV superconductors, which are singlet ones at H=0 and in the Meissner phase, and characterized by singlet-triplet mixed Copper pairs Δs+iΔt with broken symmetries in a vortex phase, is discussed. © 2006 The American Physical Society.
• Lebed, A. G. (2006). Type-IV superconductivity: Can superconductivity be more exotic than unconventional?. Journal of Low Temperature Physics, 142(3-4), 173-178.
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  Abstract: Abrikosov vortex phase in s-wave layered superconductor in a parallel magnetic field is shown to be absolutely unstable with respect to the appearance of a triplet component which breaks inversion (parity) and spin-rotational symmetries of Cooper pairs. Symmetry breaking paramagnetic effects are demonstrated to be of the order of unity if the orbital upper critical field, H c2 (0), is of the order of Clogston paramagnetic limiting field, H p. We suggest a generic phase diagram of such type-IV superconductor, which is singlet one at H=0 and in the Meissner phase and characterized by mixed singlet-triplet order parameter with broken symmetries of Copper pairs in vortex phase. A possibility to observe type-IV superconductivity in clean organic, high-Tc, and MgB 2 superconductors is discussed. © Springer Science+Business Media, Inc 2006.
• Lebed, A. G., & Bagmet, N. N. (2006). Quantum (nano-scale) limit in a parallel magnetic field in layered Q1D conductors. Journal of Low Temperature Physics, 142(3-4), 499-502.
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  Abstract: We show that electron wave functions in a quasi-one-dimensional (Q1D) layered conductor in a parallel magnetic field are always localized on conducting layers. Wave functions and electron spectrum in a quantum limit, where the "sizes" of quasi-classical electron orbits are of the order of nanoscale distances between the layers, are determined. Possible applications of our results to physical properties of Q1D materials in their superconducting and metallic phases are discussed. © 2007 Springer Science+Business Media, Inc.
• Yoshino, H., Bayindir, Z., Roy, J., Shaw, B., Ha, H., Lebed, A. G., & Naughton, M. J. (2006). Pulsed field studies of angular dependence of unconventional magnetoresistance in (TMTSF)₂ClO₄. AIP Conference Proceedings, 850, 1542-1543.
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  Abstract: The field and angle dependence of magnetoresistance of (TMTSF) 2ClO4 was studied by a pulsed magnetic field system up to 40 T. The third angular effect of this quasi-one-dimensional metal was clearly observed as well as Lee-Naughton oscillations with small amplitude for ab-plane rotation of the magnetic field. Saturating behavior of the field dependence of the magnetoresistance at a local minimum of the angular dependence contrasts with non-saturation (or divergence) at general field orientations to the crystal. This unconventional behavior may be explained by crossover of electronic system from one- to two-dimensional suggested by recent theories based on quantum mechanics. © 2006 American Institute of Physics.
• Yoshino, H., Bayindir, Z., Roy, J., Shaw, B., Ha, H., Lebed, A., & Naughton, M. J. (2006). Unconventional field dependence of magnetoresistance of (TMTSF) ₂ClO ₄ studied by 46-T pulsed magnetic field system. Journal of Low Temperature Physics, 142(3-4), 323-326.
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  Abstract: The field and angle dependence of magnetoresistance of (TMTSF) measured by a pulsed magnetic field system up to 40 T at 4.2 K to investigate its behavior at high field limit. Two minima of magnetoresistance due to the third angular effect of quasi-one-dimensional (Q1D) metals were successfully observed as well as Lee-Naughton oscillations by sub xy-plane rotation of the magnetic field. It was found that magnetoresistance tends to saturate at minima positions, while it generally diverges up to the highest magnetic field region. © Springer Science+Business Media, LLC 2006.
• Yoshino, H., Bayindir, Z., Roy, J., Show, B., Ha, H. -., Lebed, A. G., Naughton, M. J., Kikuchi, K., Nishikawa, H., & Murata, K. (2006). Pulsed magnetic field study of unconventional magnetoresistance of Q1D superconductors (TMTSF)₂ClO₄and (DMET)₂I ₃. Journal of Physics: Conference Series, 51(1), 339-342.
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  Abstract: Quasi-one-dimensional (Q1D) organic conductors with simple open Fermi surfaces have provided novel angular dependent magnetoresistance oscillation (AMRO) phenomena for the last two decades. Both semiclassical and quantum mechanical theories well explain these phenomena, but detailed study of the field dependence probably gives a crucial test. Recently it was proposed that a kind of AMRO that is known as "Lee-Naughton oscillations (LNO)" observed for (TMTSF)2ClO4 is a result of dimensional crossover of electronic system from oneto two-dimension on changing the field orientation. We have studied the field dependence of the magnetoresistance of Q1D superconductors (TMTSF)2ClO4 and (DMET) 2I3by using a 46-T pulsed magnetic field system and found the B1/2-behavior at minima of LNO. © 2006 IOP Publishing Ltd.
• Lebed, A. G. (2005). Quantum limit in a parallel magnetic field in layered conductors. Physical Review Letters, 95(24).
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  Abstract: We show that electron wave functions in a quasi-two-dimensional conductor in a parallel magnetic field are always localized on conducting layers. In particular, wave functions and the electron spectrum in a quantum limit, where the sizes of quasiclassical electron orbits are of the order of nanoscale distances between the layers, are determined. ac infrared measurements to investigate Fermi surfaces and to test Fermi-liquid theory in quasi-two-dimensional organic and high-Tc materials in high magnetic fields, Hâ‰10-45T, are suggested. © 2005 The American Physical Society.
• Lebed, A. G. (2005). Type-IV superconductivity: Cooper pairs with broken inversion and time-reversal symmetries in conventional superconductors. JETP Letters, 82(4), 204-209.
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  Abstract: The vortex phase in a singlet superconductor in the absence of impurities is shown to be absolutely unstable with respect to the appearance of a triplet component that breaks both the inversion and time-reversal symmetries of Cooper pairs. The symmetry breaking paramagnetic effects are demonstrated to be of the order of unity if the orbital upper critical field, Hc2(0), is of the order of the Clogston paramagnetic limiting field, Hp. We suggest a generic phase diagram of such a type-IV superconductor that is a singlet one at H = 0 and characterized by a mixed singlet-triplet order parameter with broken time-reversal symmetry in the vortex phase. The possibility to observe type-IV superconductivity in clean organic, high-Tc, MgB2, and other superconductors is discussed. © 2005 Pleiades Publishing, Inc.
• Lebed, A. G., Ha, H., & Naughton, M. J. (2005). Angular magnetoresistance oscillations in organic conductors. Physical Review B - Condensed Matter and Materials Physics, 71(13).
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  Abstract: We demonstrate that electron wave functions change their dimensionality at some commensurate directions of a magnetic field in conductors with open [quasi-one-dimensional (Q1D)] sheets of Fermi surface. These 1D→2D dimensional crossovers lead to delocalization of wave functions and are responsible for angular magnetoresistance oscillations. As an example, we show that suggested theory is in qualitative and quantitative agreement with the recent experimental data obtained on (TMTSF)2 ClO4 conductor. © 2005 The American Physical Society.
• Lebed, A. G., Bagmet, N. M., & Naughton, M. J. (2004). Magic angles, AMRO and interference effects in layered conductors. Journal De Physique. IV : JP, 114, 77-80.
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  Abstract: We analytically solve kinetic equation in the extended Brillouin zone and demonstrate that the interference effects which occur as electrons move along open orbits result in the appearance of Magic Angle (MA) minima of resistivity. A comparison of our theory with MA phenomena observed in resitivity component ρ⊥ (H, α), perpendicular to conducting layers in (TMTSF)2X and α -(BEDT-TTF)2MHg(SCN)4 conductors, shows a good qualitative agreement, including the first explanation why MA's with large indexes, N > 1, are observed in (TMTSF)2X (X = ClO4 and PF6) and α-(BEDT-TTF)2MHg(SCN) 4 compounds. Both physical meaning of the above mentioned interference effects and mathematical expressions for ρ⊥ (H, α) are different from that in a so-called OsadaÕs model. © EDP Sciences,.
• Lebed, A. G., Bagmet, N. N., & Naughton, M. J. (2004). Magic angle effects and angular magnetoresistance oscillations as dimensional crossovers. Physical Review Letters, 93(15), 157006-1-157006-4.
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  PMID: 15524929;Abstract: The effects of magic angle (MA) and magnetoresistance oscillations as dimensional crossovers, were investigated. The interference effects between velocity and density of states, which occur as electrons move along open orbits in the Brillouin zone in anisotropic conductors, were observed to change the dimensionality of wave function at MA directions. It was observed that 1D → 2D dimensional crossovers resulted in appearance of sharp minima. The results show that MA and angular magnetoresistance osciilations occurred due to the existence of quai-one-dimensional sheets of Fermi surface.
• Lebed, A. G. (2003). Theory of magnetic field-induced charge-density-wave phases. JETP Letters, 78(3), 138-142.
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  Abstract: We elaborate an analytical theory of a cascade of magnetic field-induced charge-density-wave (FICDW) phases. It is shown that the following features distinguish it from the well-known spin-density-wave cascade: (1) the FICDW phases exist at temperatures much lower than the characteristic CDW transition temperature at H = 0; (2) the cascade of the FICDW phases dramatically changes at certain directions of a magnetic field due to an interplay of Zeeman spin-splitting and electron motion along open Fermi surfaces. Theoretical results are compared with the recent experimental attempts to reveal FICDW phases in the organic conductors α-(ET)2MHg(SCN)4 (M = K, Tl, Rb, etc.). © 2003 MAIK "Nauka/Interperiodica".
• Lebed, A. G., & Naughton, M. J. (2003). Interference Commensurate Oscillations in Quasi-One-Dimensional Conductors. Physical Review Letters, 91(18), 1870031-1870034.
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  PMID: 14611308;Abstract: The angular magnetoresistance oscillations in quasi-one-dimensional conductors were discussed. The origin of the oscillations were related to the interference effects resulting from Bragg reflections which occured as electrons move along quasiperiodic and periodic electron trajectories in the extended Brillouin zone. Two most genaral electron trajectories, characterised by θ and φ were considered which corresponded commensurate oscillations and generalized Danner-Kang-Chaikin (DKC). It was shown that the commensurate directions of a magnetic field corresponded to the minima at large enough φ whereas smaller minima occurred for only odd values of N depending in the particluar value of φ.
• Lebed, A. G. (2002). Field-induced spin-density-wave phases in quasi-one-dimensional conductors: Theory versus experiments. Physical Review Letters, 88(17), 1770011-1770014.
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  PMID: 12005777;Abstract: The field-induced spin-density-wave phases (FISDW) were studied in quasi-one-dimensional conductors. It was showed that the important features of the magnetic field induced-FISDW phase diagrams were missed by the quantized nesting model. It was speculated that the 3D quantum Hall effect (QHE) existed only in the quantum FISDW phases and disappeared in the quasiclassical FISDW states. It was expected that physical properties as a nonlinear FISDW conductivity and magic angle phenomenon were different in the quantum FISDW and quasiclassical FISDW phases.
• Lebed, A. G. (2002). Magnetic tests to reveal triplet supeconductivity in (TMTSF)₂PF₆ and a possible breaking of a time reversal symmetry in Sr₂RuO₄, LBCO, and YBCO. International Journal of Modern Physics B, 16(20-22), 3198-.
• Lebed, A. G. (2002). Triplet superconductivity order parameter in an organic superconductor (TMTSF)₂PF₆. International Journal of Modern Physics B, 16(20-22), 3271-.
• Lebed, A. G., & Naughton, M. J. (2002). Fermi surface interference effects and angular magnetic oscillations in Q1D conductors. Journal De Physique. IV : JP, 12(9), Pr9/369-Pr9/372.
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  Abstract: We have derived a common analytical expression to describe angular magnetic oscillations observed in quasi-one-dimensional (Q1D) conductors (TMTSF)2X and (DMET)2I3. Among these are the Danner et al. oscillations, the "third angular effect", and very rich angular oscillations discovered by Lee et al. The physical meaning of the latter oscillations is shown to be related to interference effects.
• Lebed, A. G. (2000). Does the "quantized nesting model" properly describe the magnetic-field-induced spin-density-wave transitions?. JETP Letters, 72(3), 141-143.
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  Abstract: Theoretical reinvestigation of a so-called field-induced spin-density-wave (FISDW) phase diagram in a magnetic field in quasi-one-dimensional compounds (TMTSF)2X (X = PF6, ClO4, AsF6, etc.) has revealed some novel qualitative features. Among them are (1) the FISDW wave vector is never strictly quantized; and (2) the FISDW phase diagram consists of two regions: (a) "Quantum FISDW," where there exist jumps of the FISDW wave vectors between different FISDW subphases and (b) "Quasiclassical FISDW," where the jumps disappear above some critical points and only one FISDW phase (characterized by a wave vector oscillating with a magnetic field) exists. Both these features are due to taking account of the breaking of an electron-hole symmetry. They contradict the previous textbook theoretical results (including the calculations of the "Three Dimensional Quantum Hall Effect") performed by means of the "Quantized Nesting Model" which explicitly assumes the existence of the electron-hole symmetry. We stress that some effects related to the phenomena described above were experimentally observed but not properly interpreted. © 2000 MAIK "Nauka/Interperiodica".
• Lebed, A. G. (2000). Possible triplet order parameter in a Q1D organic superconductor (TMTSF)₂PF₆. Physica C: Superconductivity and its Applications, 341-348(PART 2), 1699-1700.
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  Abstract: We point out that (TMTSF)2PF6 compound at P ≃ 6 kbar is possibly a triplet superconductor with the vector order parameter d = (dx ≠ 0, dy ,dz = 0). It corresponds to an anisotropic spin susceptibility in a superconducting state: χb′(z) = χ0, χa(x) ≠ χ0, where χ0 is its value in a metallic phase. (Here, the spin quantization axis, z, is parallel to the easy axis, b′, of an antiferromagnetic SDW phase existing at P = 0). It is shown that the suggested order parameter can explain why the upper critical field along b′-axis (I.J. Lee, M.J. Naughton, G. Danner, and P.M. Chaikin, Phys. Rev. Lett. 78, 3555 (1997)) exceeds all paramagnetic limiting fields (including that for a non-uniform superconductivity) whereas the upper critical field along the a-axis is restricted by the Pauli paramagnetic effects. The triplet order parameter is consistent with the earlier results on a destruction of superconductivity by nonmagnetic impurities and the absence of the Hebel-Slichter peak in the NMR data as well as with the recent Knight shift measurements by S. Brown et al and by I. J. Lee et al. © 2000 Elsevier Science B.V. All rights reserved.
• Lebed, A. G., & Hayashi, N. (2000). Paramagnetic-like destructive mechanism against superconductivity in Sr₂RuO₄: A triplet scenario versus a singlet one. Physica C: Superconductivity and its Applications, 341-348(PART 2), 1677-1678.
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  Abstract: The most popular description of superconductivity phenomenon in Sr2RuO4 is based on a so-called single-band (usually γ-band) "isotropic p-wave order parameter". In a magnetic field parallel to the conducting planes, such triplet "isotropic p-wave phase" is not destroyed by the Clogston-Chandrasekhar paramagnetic limiting field and can be destroyed only by the Meissner currents (i.e., the orbital effects). We analyze the orbital destructive effects against superconductivity for in-plane magnetic field (when electron orbits are open) and find that Hc2∥(0) ≃ 0.75 Tc(dHc2∥(T)/dT)Tc (which is a little bigger than the Werthamer-Helfand-Hohenberg value for an isotropic 3D case). We point out that the experimentally determined ratio Hc2∥(0)/Tc(dHc2∥(T)/dT)Tc ≃ 0.44 - 0.5 in Sr2RuO4 is significantly less than the calculated value 0.75. Since the upper critical field, Kc2∥(T). is a well experimentally defined quantity in Sr2RuO4 (unlike high-Tc superconductors) we conclude that the single-band triplet "isotropic p-wave order parameter" seems to be inappropriate description of superconductivity in this material. Two possibilities are discussed: 1) Three-band nature of triplet superconductivity; 2) Singlet (d-wave) nature of superconducting pairing (in this case, the destructive actions of both the orbital effects and the Clogston-Chandrasekhar paramagnetic effects result in an agreement with the experimentally observed value of Hc2∥(0)/Tc(dHc2∥(T)/dT)Tc). © 2000 Elsevier Science B.V. All rights reserved.
• Lebed, A. G., Machida, K., & Ozaki, M. (2000). Triplet electron pairing and anisotropic spin susceptibility in organic superconductors (TMTSF)₂X. Physical Review B - Condensed Matter and Materials Physics, 62(2), R795-R798.
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  Abstract: We argue that the (TMTSF)2PF6 compound under pressure is likely a triplet superconductor with a vector order parameter d(k)=(da(k)≠0, dc(k)=?, d′(k)=0); |da(k)|>|dc(k)|. It corresponds to an anisotropic spin susceptibility at T=0: χb′=χ0, χa≪χ0, where χ0 is its value in a metallic phase. (The spinquantization axis, z, is parallel to a so-called b′ axis.) We show that the suggested order parameter explains why the upper critical field along the b′ axis exceeds all paramagnetic limiting fields, including that for a nonuniform superconducting state, whereas the upper critical field along the a axis (a⊥b′) is limited by the Pauli paramagnetic effects [I. J. Lee, M. J. Naughton, G. M. Danner, and P. M. Chaikin, Phys. Rev. Lett. 78, 3555 (1997)]. The triplet order parameter is in agreement with the recent Knight shift measurements by I. J. Lee et al. as well as with the early results on a destruction of superconductivity by nonmagnetic impurities and on the absence of the Hebel-Slichter peak in the NMR relaxation rate. ©2000 The American Physical Society.
• Lebed, A. G. (1999). Gap symmetry and a revival of superconductivity in high parallel magnetic fields in Q2D and Q1D organic, high-T_c, and Sr₂RuO ₄ compounds. Journal of Superconductivity and Novel Magnetism, 12(3), 453-458.
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  Abstract: From the BCS theory, we derive an equation determining the upper critical field, Hc2(T), parallel to conducting planes of both layered Q2D and Q1D superconductors. It extends the quasiclassical Ginzburg-Landau-Abrikosov- Gor'kov (GLAG) and Lawrence-Doniach descriptions of Hc2(T) to the case of high magnetic fields where the quantum nature of an electron motion along open Fermi surfaces is important. This equation demonstrates two new phenomena: (1) a complete restoration of superconductivity at H ≃ H c5 > Hc2(0) in the case of p-wave pairing of electrons; (2) a surviving of superconductivity at Hc2(0) < H < H p* in the case of s(d)-wave pairing, where Hp* ≠ Hp [Here, Hc2(0) and Hp are the quasiclassical GLAG upper critical field and the paramagnetic Clogston-Chandrasekhar limiting field, correspondingly; Hc5 and Hp* are defined in the text]. Our analysis of recent experimental data on (TMTSF)2PF6 by I. J. Lee et al. and M. J. Naughton et al. shows that superconductivity significantly exceeds H p*. This demonstrates a strong suppression of the Pauli pair-breaking effects and may reflect a p-wave pairing of electrons. We propose to measure Hc2(T) in Sr2RuO4 (which is believed to be a p-wave superconductor) to prove a symmetry of a superconducting order parameter. © 1999 Plenum Publishing Corporation.
• Lebed, A. G. (1999). Revival of superconductivity in high magnetic fields and a possible p-wave pairing in (TMTSF)₂PF₆. Physical Review B - Condensed Matter and Materials Physics, 59(2), R721-R724.
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  Abstract: From the BCS theory, we derive an equation which accounts for quantum effects of an electron motion along open Fermi surfaces and determines the upper critical field Hc2⊥(T) perpendicular to the chains of a quasi-one-dimensional conductor. This equation demonstrates two unusual phenomena: (1) restoration of superconductivity at H>Hc2⊥(0) in p-wave superconductors, where Hc2⊥(0) is the quasiclassical upper critical field; (2) surviving of superconductivity at Hc2⊥(0), Hp
• Lebed, A. G., & Yamaji, K. (1998). Restoration of superconductivity in high parallel magnetic fields in layered superconductors. Physical Review Letters, 80(12), 2697-2700.
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  Abstract: We derive an equation determining the upper critical field Hc2∥(T) parallel to conducting planes of a layered superconductor from the BCS theory. It extends the descriptions of Hc2∥(T) within the Ginzburg-Landau-Abrikosov-Gor'kov theory and the Lawrence-Doniach model to the case of strong magnetic fields. From this equation, it follows that orbital effects of an electron motion along an open Fermi surface in a magnetic field start to restore superconductivity at magnetic fields higher than the quasiclassical upper critical field and result in the appearance of a reentrant phase with Tc(H) ≃ Tc(0). A stability of the reentrant phase against fluctuations is discussed.
• Lebed, A. G. (1997). Ground state of (TMTSF)₂ClO₄ in high magnetic fields: The creation of Su-Schrieffer-Heeger solitons. Physical Review B - Condensed Matter and Materials Physics, 55(3), 1299-1302.
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  Abstract: It is shown that the problem of spin-density-wave formation in a quasi-one-dimensional organic conductor (TMTSF)2ClO4 in a magnetic field is equivalent to Brazovskii-Dzyaloshinskii-Kirova variant of an exactly solvable one-dimensional problem of Su-Schrieffer-Heeger (SSH) solitons. We demonstrate that the ground state in (TMTSF)2ClO4 in high magnetic fields corresponds to SSH solitonic superstructure. We calculate the magnetic moment and energy gap in an electron spectrum and discuss recent experimental data in terms of the creation of SSH solitonic superstructure.
• Lebed, A. G. (1997). New aspects of non-Fermi-liquid behaviour in Q1D metals. Synthetic Metals, 85(1-3), 1615-1616.
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  Abstract: The second order corrections to magnetic moment, M, magnetic susceptibility, χ, and specific heat, C, due to electron-electron ("e-e") interactions are calculated in a Q1D conductor (TMTSF)2ClO4 in a metallic phase. Strong magnetic oscillations of these thermodynamical quantities are found to exist due to the oscillations of matrix elements of "e-e" interactions in the Peierls channel under the condition of magnetic breakdown. We note that the frequency of the oscillations corresponds to open ("interference") orbits that contradicts Fermi liquid description of quasiparticles. We demonstrate that the relative magnitudes of these forbidden oscillations are anomalously large: δχ/χ0 ∼ 1 - 10, δM/M0 ∼ 10-1, and δC/C0 ∼ 10-2.
• Lebed, A. G., & Bagmet, N. M. (1997). Non-analytical magnetoresistance and a new method of investigation of Fermi surfaces in Q2D and Q1D conductors. Synthetic Metals, 85(1-3), 1493-1494.
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  Abstract: We demonstrate that transverse magnetoresistance is a non-analytical function of a magnetic field, ρ⊥ ∼ |H|1/2, if a magnetic field is normal to quasi-two-dimensional (Q2D) Fermi surface (FS) at an inflexion point. Recently discovered Osada-Kagoshima angular resonance is described in terms of the existence of an inflexion point on the FS of (TMTSF)2ClO4-conductor. It is shown that at arbitrary direction of a magnetic field in a 2D plane transverse magnetoresistance does not depend on electron relaxation time and obeys a linear law, ρ⊥ ∼ A|H|, where A depends on some local characteristics of a Q2D FS. The above mentioned effects provide us with a new method of investigation of FS's in strongly anisotropic Q2D (Q1D) conductors.
• Lebed, A. G., & Bagmet, N. N. (1997). Nonanalytical magnetoresistance, the third angular effect, and a method to investigate Fermi surfaces in quasi-two-dimensional conductors. Physical Review B - Condensed Matter and Materials Physics, 55(14), R8654-R8657.
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  Abstract: We demonstrate that transverse magnetoresistance is a nonanalytical function of the magnetic field, ρ⊥(H)∼|H|1/2, if a magnetic field is parallel to the plane of anisotropy and normal to the Fermi surface at an inflection point in a quasi-two-dimensional (Q2D) conductor. The so-called "third angular effect," recently discovered in organic conductors (TMTSF)2X (X=ClO4,PF6) and (DMET)2I3, is interpreted in terms of the existence of an inflection point on their Fermi surfaces. Nonanalytical magnetoresistance is predicted to appear when the magnetic field is applied at the "third magic angles," Θ=±Θc. It is also shown that at arbitrary directions of the in-plane magnetic field the magnetoresistance does not depend on relaxation time and obeys the law ρ⊥(H)∼A|H| with factor A being a function of local characteristics of a Q2D Fermi surface. The above-mentioned phenomena provide useful methods to investigate Fermi surfaces in strongly anisotropic Q2D conductors including organic and high-Tc superconductors.
• Lebed, A. G., & Yamaji, K. (1997). Restoration of superconductivity at high magnetic fields in layered high-T_c and organic superconductors. Physica C: Superconductivity and its Applications, 282-287(PART 3), 1859-1860.
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  Abstract: An integral equation determining the upper critical field parallel to the conducting plane of a layered superconductor is derived from microscopic BCS theory. From this equation, it follows that the superconductivity-destruction mechanism due to the orbital effect becomes ineffective at magnetic fields higher than a critical field Hc4 due to a quantum nature of an electron motion in a magnetic field. This leads to the appearance of reentrant superconducting phase with dTc/dH > 0 in the case of p-pairing and under certain conditions in the case of s(d)-pairing. We also show that the orbital effect cannot destroy superconductivity at T = 0 at arbitrary magnetic fields. Therefore qualitative deviations from the description of GLAG (WHH) theory have to appear for arbitrary symmetry of the order parameter at low enough temperatures. We argue that p(s)-wave superconductor Sr2RuO4 as well as s(d)-wave superconductors TlBa2CaCu2O7, Tl2Ba2Ca3Cu4Ox, β-(ET)2AuI2, and κ-(ET)2I3 are good candidates for the observation of the above mentioned phenomena.
• Sasaki, T., Lebed, A. G., Fukase, T., & Toyota, N. (1997). Magnetic field response of the spin density wave in α-(BEDT-TTF)₂KHg(SCN)₄. Synthetic Metals, 86(1 -3 pt 3), 2063-2064.
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  Abstract: Magnetic phase diagram and metal - spin-density-wave (SDW) transition in an organic conductor α-(BEDT-TTF)2KHg(SCN)4 are revisited from a view point of magnetic torque measurements. The metal - SDW transition temperature determined by magnetic torque measurements shifts from about 8K at H = O T to higher temperatures with increasing magnetic field, and tends to be saturated. This transition line is different from that determined by the so-called kink structure of the magnetoresistance so far. Inside the SDW phase, an additional phase boundary exists at the temperature independent field of 23 T, where the effective mass and Dingle temperature determined by de Haas - van Alphen oscillations change their values.
• Sasaki, T., Lebed, A. G., Fukase, T., & Toyota, N. (1997). Magnetic field response of the spin density wave in α-(BEDT-TTF)₂KHg(SCN)₄. Synthetic Metals, 86(1-3), 2063-2064.
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  Abstract: Magnetic phase diagram and metal - spin-density-wave (SDW) transition in an organic conductor α-(BEDT-TTF)2KHg(SCN)4 are revisited from a view point of magnetic torque measurements. The metal - SDW transition temperature determined by magnetic torque measurements shifts from about 8K at H = 0 T to higher temperatures with increasing magnetic field, and tends to be saturated. This transition line is different from that determined by the so-called kink structure of the magnetoresistance so far. Inside the SDW phase, an additional phase boundary exists at the temperature independent field of 23 T, where the effective mass and Dingle temperature determined by de Haas - van Alphen oscillations change their values.
• Lebed, A. G. (1996). Magnetic oscillations in a normal state of organic conductors: Many-body approach. Journal de Physique I, 6(12), 1819-1836.
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  Abstract: We argue that magnetic and angular oscillations observed in quasi-one-dimensional (Q1D) organic conductors represent a new type of many-body phenomena. The physical nature of such effects as "magic angles" in (TMTSF)2ClO4, (TMTSF)2PF6, and (DMET-TSeF)2 AuCl2 as well as "rapid magnetic oscillations" in (TMTSF)2ClO4 is shown to be beyond the standard theory of metals. Below we discuss an explanation of these phenomena which utilizes unusual many-body effect - a change of an effective dimensionality of electron-electron ("e-e") interactions with changing both a magnitude and a direction of a magnetic field. We show that some exotic transport properties of a metallic state can be interpreted in terms of these dimensional crossovers. We also demonstrate that magnetic field dependence of "e-e" interactions has to break Fermi liquid description of quasiparticles at high magnetic fields, H ≥ 25 - 30 T. This leads to the appearance of strong forbidden oscillations of magnetic susceptibility, δχ/χ0 ∼ 1-10, and magnetic moment, δM/M0 ∼ 0.1. All of the above mentioned unique properties of a metallic phase in (TMTSF)2X and (DMET-TSeF)AuCl2 allow us to call it an anomalous metallic phase. © Les Éditions de Physique 1996.
• Sasaki, T., Lebed, A. G., Fukase, T., & Toyota, N. (1996). Interplay of the spin-density-wave state and magnetic field in the organic conductor α-(BEDT-TTF)₂KHg(SCN)₄. Physical Review B - Condensed Matter and Materials Physics, 54(18), 12969-12978.
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  Abstract: Magnetic phase diagram of a quasi-two-dimensional organic conductor α-(BEDT-TTF)2KHg(SCN)4 is revisited from a viewpoint of magnetic torque measurements in high fields up to 30 T. A phase boundary that is interpreted as a metal-spin density wave (SDW) phase transition is found by using torque measurements. It is shown that this phase boundary is clearly distinguished from so-called kink transition of the magnetoresistance. We demonstrate that the transition temperature defined by the midpoint of the broad phase transition is almost independent on magnetic field up to 23 T. Onset temperature of the transition shifts from about 8 K at H=0T to higher temperatures with increasing of a magnetic field, and tends to be saturated. The onset line of this transition follows well the theoretical expectation that SDW has to be stabilized by a magnetic field. This allows us to estimate such important band parameters of the quasi-one-dimensional section of the Fermi surface as an effective mass, mID≃(0.5±0.1)m0, and an upper limit of an imperfect nesting bandwidth tc′≃( 10 ± 1 ) K. The other phase boundaries determined by the position of the kink and hysteresis properties of the magnetoresistance are interpreted as subphases inside the SDW phase. Inside the SDW phase, we find an additional phase boundary at the temperature-independent field of 23 T, which corresponds to the appearance of de Haas-van Alphen oscillations on a magnetic torque curve. At the 23 T boundary, both the effective mass, m*, and the Dingle temperature, TD, change their values from m*=(1.67 ± 0.05) m0 and TD=3.7-4.0 K in low magnetic field region to (1.95 ± 0.05) m0 and 2.5-2.8 K in high field region. The latter phenomenon is discussed in terms of a reconstruction of the Fermi surface due to the SDW formation. Hysteresis of the magnetoresistance observed in one of the subphases inside the SDW phase is studied in detail by measuring both the temperature and the magnetic field dependences.
• Gor'kov, L., & Lebed, A. G. (1995). Anion gap and stability of the metallic phase for (TMTSF)₂ClO₄. Synthetic Metals, 70(1 -3 pt 2), 727-730.
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  Abstract: Starting with the prototype nesting spectrum of (TMTSF)2PF6, it is emphasized that the gap due to anion ordering (AO) would result in a somewhat different SDW state for ClO4 if the 'antinesting' term, t′b, was omitted. The field then first diminishes that term, improving nesting. At the same time the field decreases pairing between subbands with nesting features because of the difference in the symmetry of their wavefunctions. This leads to the reentrance of the metallic state. The magnetic breakdown (MB) gradually decreases the effect of AO. Properties of the 'prototype' PF6-material are expected to be seen again at large magnetic fields. However, it occurs in a peculiar phase diagram with sharp spikes in TSDW periodic in the inverse magnetic field, 1/H. Cyclotron resonance on open orbits is discussed to study whether the 'transverse' gap due to AO in (TMTSF)2ClO4 manifests itself in other properties.
• Gor'kov, L., & Lebed, A. G. (1995). Anion gap and stability of the metallic phase for (TMTSF)₂ClO₄. Synthetic Metals, 70(1-3), 727-730.
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  Abstract: Starting with the prototype nesting spectrum of (TMTSF)2PF6, it is emphasized that the gap due to anion ordering (AO) would result in a somewhat different SDW state for ClO4 if the "antinesting" term, t′b, was omitted. The field then first diminishes that term, improving nesting. At the same time the field decreases pairing between subbands with nesting features because of the difference in the symmetry of their wavefunction. This leads to the reentrance of the metallic state. The magnetic breakdown (M B) gradually decreases the effect of AO. Properties of the "prototype" PF6-material are expected to be seen again at large magnetic fields. However, it occurs in a peculiar phase diagram with sharp spikes in TSDW periodic in the inverse magnetic field, 1/H. Cyclotron resonance on open orbits is discussed to study whether the "transverse" gap due to AO in (TMTSF)2ClO4 manifests itself in other properties. © 1995.
• Gor'kov, L., & Lebed, A. G. (1995). Fast oscillations in the surface impedance of (TMTSF)2ClO4 in a magnetic field. Physical Review B, 51(2), 1362-1365.
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  Abstract: The energy gap due to anion ordering introduces essential differences for electrons of two particular subbands in a magnetic field. The magnetic breakdown restores the behavior of the prototype PF6 in an irregular manner as the field increases. The fast oscillations (periodic in 1/H) appear to be due to the fact that the electron trajectories in ClO4 coincide with those in PF6 only at specific values of H. The fast oscillations superimpose on the cyclotron-resonance-type singularities. © 1995 The American Physical Society.
• Gorkov, L. P., & Lebed, A. G. (1995). Metal-phase stability of (TMTSF)2ClO4 in high magnetic fields, where TMTSF is tetramethyltetraselenafulvalene. Physical Review B, 51(5), 3285-3288.
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  Abstract: The field-induced spin-density-wave state in (TMTSF)2ClO4, where TMTSF is tetramethyltetraselenafulvalene, develops because the field diminishes the antinesting terms, tb, to restore the spin-density wave (SDW) that would exist at tb=0 despite the anion gap in ClO4. The gap changes the wave functions symmetry for nested subbandsone of them changes sign upon crossing the new zone boundary, destroying the coherence of paired electrons at H 0. Competition between the two phenomena leads to a reentrance of the metallic state. Magnetic breakdown is unable to restore a PF6-type ground state and reveals itself in a pattern of peaks for TSDW(H) periodic in H-1. © 1995 The American Physical Society.
• Lebed, A. G. (1995). Magic angles effects and rapid magnetic oscillations in organic superconductors. Synthetic Metals, 70(1 -3 pt 2), 993-996.
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  Abstract: In the framework of the quantum approach to electron-electron ('e-e')·interactions in a magnetic field, two related phenomena, 'magic angles' and 'rapid magnetic oscillations', are investigated. We show that the sharp angular magnetoresistance dips have to exist at the main 'magic angles' in Q1D metals due to the unusual dependence of 'e-e' - scattering on the direction of the magnetic field. We suggest that 'rapid magnetic oscillations' are the result of the influence of a magnetic breakdown on 'e-e'-scattering. Our calculations are in qualitative agreement with experimental data.
• Lebed, A. G. (1995). Magic angles effects and rapid magnetic oscillations in organic superconductors. Synthetic Metals, 70(1-3), 993-996.
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  Abstract: In the framework of the quantum approach to electron-electron ("e-e")• interactions in a magnetic field, two related phenomena, "magic angles" and "rapid magnetic oscillations", are investigated. We show that the sharp angular magnetoresistance dips have to exist at the main "magic angles" in Q1D metals due to the unusual dependence of "e-e" - scattering on the direction of the magnetic field. We suggest that "rapid magnetic oscillations" are the result of the influence of a magnetic breakdown on "e-e"-scattering. Our calculations are in qualitative agreement with experimental data. © 1995.
• Lebed, A. G. (1995). New type of quantum magnetic resistance oscillations in quasi-one-dimensional conductors. Physical Review Letters, 74(24), 4903-4906.
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  Abstract: We suggest an explanation for the "rapid magnetic oscillations" (RMO) in the metallic phase of the organic superconductor (TMTSF)2C1O4. It is based on the possibility of quantum magnetic oscillations in the probability of electron-electron scattering and thus exceeds the bounds of the standard description of the magnetic oscillations in metals. The calculated RMO frequency is in agreement with experimental data. The estimated temperature and magnetic field dependences of RMO magnitude are unusual.
• Gor'kov, L., & Lebed', A. (1993). Cyclotron resonance on open orbits in organic materials. Physical Review Letters, 71(23), 3874-3877.
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  Abstract: The cyclotron resonance on open orbits is suggested to demonstrate the one dimensional character of electron motion along the main conducting axis in the presence of a perpendicular magnetic field for organic materials with warped open Fermi surfaces. Singular behavior at resonant frequencies in the surface impedance and the helicon waves spectrum are obtained.
• Lebed, A. G. (1993). New type of magnetic resonance and giant quasi-one-dimensional fluctuations in organic superconductors. Synthetic Metals, 57(2 -3 pt 6), 4691-4696.
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  Abstract: We consider the fluctuation contribution to free energy of a quasi-one-dimensional (Q1D) metal due to electron-electron (`e-e') interaction in magnetic field. Electron paramagnetic momentum is found to become strongly temperature and pressure dependent in a broad temperature region, T≤200 K. Electron specific heat also has large fluctuation correction and exhibit nontrivial temperature behaviour. As a result of the influence of Zeeman-splitting on processes of `e-e'-scattering, new angular oscillations of specific heat occur in magnetic field.
• Lebed, A. G. (1993). New type of magnetic resonance and giant quasi-one-dimensional fluctuations in organic superconductors. Synthetic Metals, 57(2-3), 4691-4696.
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  Abstract: We consider the fluctuation contribution to free energy of a quasi-one-dimensional (Q1D) metal due to electron-electron ("eee") interaction in magnetic field. Electron paramagnetic momentum is found to become strongly temperature and pressure dependent in a boad temperature region, T{less-than or approximate} 200K. Electron specific heat also has large fluctuation correction and exhibit nontrivial temperature behaviour. As a result of the influence of Zeeman-splitting on processes of "e-e"-scattering, new angular oscillations of specific heat occur in magnetic field. © 1993.
• Lebed, A. G. (1991). New phase transitions in the organic superconductor (TMTSF)₂ClO₄. Synthetic Metals, 42(1-2), 1938-.
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  Abstract: The stability of spin-density wave formation in the organic superconductor (TMTSF)2ClO4 is studied. The anion gap in the electron spectrum causes reentrance of the metallic state in high magnetic fields. It also leads to fast oscillations of physical properties, in particular the phase transition temperature, versus magnetic field. Both these phenomena have been observed experimentally. © 1991.
• Lebed, A. G. (1991). New phases and quantum Hall effect in organic superconductors. Physica B: Condensed Matter, 169(1 -4 pt 3), 368-371.
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  Abstract: 'Umklapp processes' in quasi-one-dimensional conductors (TMTSF)2X change their phase diagram qualitatively in the magnetic field. This leads to the coexistence of spin-density waves (SDW) characterized by different wave vectors. Earlier calculations on the quantum Hall effect in this situation appear to be incorrect and the Hall conductivity quantization follows from a more general theorem.
• Lebed, A. G. (1991). New phases and quantum Hall effect in organic superconductors. Physica B: Physics of Condensed Matter, 169(1-4), 368-371.
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  Abstract: "Umklapp processes" in quasi-one-dimensional conductors (TMTSF)2X change their phase diagram qualitatively in the magnetic field. This leads to the coexistence of spin-density waves (SDW) characterized by different wave vectors. Earlier calculations on the quantum Hall effect in this situation appear to be incorrect and the Hall conductivity quantization follows from a more general theorem. © 1991.
• Lebed, A. G., & Landau, L. D. (1991). New phase transitions in the organic superconductor (TMTSF)₂ClO₄. Synthetic Metals, 42(1-2), 1938-.
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  Abstract: The stability of spin-density wave formation in the organic superconductor (TMTSF)2ClO4 is studied. The anion gap in the electron spectrum causes reentrance of the metallic state in high magnetic fields. It also leads to fast oscillations of physical properties, in particular the phase transition temperature, versus magnetic field. Both these phenomena have been observed experimentally.
• Lebed, A. G., & Bak, P. (1989). Theory of reentrance of spin-density-wave transitions in bis-tetramethyltetraselenafulvalenium perchlorate [(TMTSF)2ClO4]. Physical Review B, 40(16), 11433-11436.
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  Abstract: The stability of spin-density-wave formation in the organic superconductor bis-tetramethyltetraselenafulvalenium perchlorate (TMTSF)2ClO4 is studied. The anion gap in the electron spectrum causes reentrance of the metallic state in high magnetic fields. It also leads to fast oscillations of physical properties, in particular, the phase-transition temperature versus magnetic field. Both these phenomena have been observed experimentally. © 1989 The American Physical Society.
• Lebed, A. G., & Bak, P. (1989). Theory of unusual anisotropy of magnetoresistance in organic superconductors. Physical Review Letters, 63(12), 1315-1317.
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  Abstract: We suggest that weak electron tunneling between layers is responsible for the experimentally observed dramatic deviations from two-dimensional behavior in the magnetoresistance in the metallic phase of the quasi-two-dimensional conductors (TMTSF)2ClO4 and (TMTSF)2PF6. We predict a fine structure due to resonances in open orbits between motion parallel and perpendicular to the planes. © 1989 The American Physical Society.
• Burlachkov, L. I., Gor'kov, L., & Lebed', A. (1987). IDENTIFICATION OF THE SUPERCONDUCTIVITY TYPE IN ORGANIC SUPERCONDUCTORS.. Europhysics Letters, 4(8), 941-946.
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  Abstract: Two phenomena are pointed out which, if observed, would testify that the superconductivity in the Bechgaard salts belongs to the triplet pairing: excitation of the spin waves in the radio-frequency fields and the superconductivity restoration in high enough magnetic fields H parallel b*.
• Burlachkov, L. I., Gor'kov, L., & Lebed', A. (1987). On the superconductivity type in the Bechgaard salts. Physica B+C, 148(1-3), 500-502.
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  Abstract: The existence of the spin waves and the superconductivity restoration in high enough magnetic fields are predicted in case of the triplet pairing in the Bechgaard salts. © 1987.
• Gor'kov, L., & Lebed', A. (1984). ON THE STABILITY OF THE QUASI-ONE-DIMENSIONAL METALLIC PHASE IN MAGNETIC FIELDS AGAINST THE SPIN DENSITY WAVE FORMATION.. Journal de physique. Lettres, 45(9), 433-440.
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  Abstract: For a simple anisotropic metal model with two open nested Fermi surfaces, it is shown that the tendency to spin density wave formation increases when a magnetic field is applied, which could lead to a series of phase transitions as functions of the field value. The results are suggested as an explanation of the phase diagram of the (TMTSF)//2X compounds.

Presentations

• Lebed, A. G. (2021, April). Breakdown of the Equivalence Principle for a Quantum Body. April Meeting of American Physical Society. Online: APS.
• Lebed, A. G. (2021, July). Breakdown of the Equivalence Principle for a composite quantum body. 16th Marcel Grossmann meeting. Online.
• Lebed, A. G. (2021, July). Breakdown of the Equivalence Principle for a quantum body. Physical Interpretations of Relativity Theory - 2021. Online.
• Lebed, A. G. (2021, March). Restoration of superconductivity in high magnetic fields in UTe2. March Meeting of Americal Physical Society. Online: APS.
• Lebed, A. G. (2020, Summer). Inequivalence between gravitational mass and energy for quantum body. RUSGRAV-17 (International conference on gravitation, cosmology, and astrophysics). St. Petersburg, Russia.
• Lebed, A. G. (2019, July). Inequivalence between gravitation and inertial masses. Physical Interpretations of Relativity Theory - 2019. Bauman Moscow State Technical University 5, 2-nd Baumanskaya street, Moscow, 105005 Russia.
• Lebed, A. G. (2019, June). Some many-body phenomena due to quantum and quasiclassical effects of electron motion along open trajectories in a magnetic field. Modern Trends in Condensed Matter Physics (Lev Gor'kov Memorial Conference). Chernogolovka, Russia.
• Lebed, A. G. (2018, July). Inequivalence of active gravitational mass and energy due to quantum effects. !5th Marcel Grossmann International Conference. Rome, Italy.
• Lebed, A. G. (2018, October). Breakdown of the equivalence between gravitational mass and energy. Invited Colloqium at Boston College. Boston, MA, USA.
• Lebed, A. G. (2017, January). Inequivalence between Gravitational Mass and Energy for a Quantum Body. Testing Gravity 2017. Vancouver, Canada.
• Lebed, A. G. (2017, March). Inequality between Gravitational and Inertial Masses: Suggested Experiment on the Earth’s Orbit. 2017 IEEE Aerospace Conference. Big Sky, Montana, USA.
• Lebed, A. G. (2017, Spring). Inequality between Gravitational and Inertial Masses. Cooquium at Physis Department of UofA. Tucson, AZ, USA.
• Lebed, A. G. (2016, July). Inequivalence between active gravitational mass and energy for a quantum body. 21st International Conference on General Relativity and Gravitation. New York City.
• Lebed, A. G. (2016, March). Possible existence of superconductivity in ultra-high magnetic fields. American Physical Society March Meeting. Baltimore.
• Lebed, A. G. (2015, August). Possible triplet superconductivity and its main features in the quasi-one-dimensional conductor Li(0.9)Mo(6)O(17). Materials and Mechanisms of Superconductivity (M2S-2015). Geneva, Switzerland: National Science Foundation.
• Lebed, A. G. (2015, March/Spring). Possible restoration of superconductivity in the quasi-one-dimensional conductor Li$_{0.9}$Mo$_6$O$_{17}$ in pulsed high magnetic field $H\approx 100$ T. March Meeting of the American Physical Society. San Antonio, Texas, USA: National Science Foundation.
• Lebed, A. G. (2014, April). Breakdown of the Equivalence between Gravitational Mass and Energy. April Meeting of the American Physical Society. Savannah, GA, USA.
• Lebed, A. G. (2014, August). Quantum Limit for Triplet Superconductivity in a Quasi-One-Dimensional Conductor. ISCOM-2014. Cargese, Corsica, France.
• Lebed, A. G. (2014, March). Possible Restoration of Triplet Superconductivity in High Magnetic Fields. March Meeting of the American Physical Society. Denver, CO, USA.