[show abstract][hide abstract] ABSTRACT: Two-dimensional electron gas (2DEG) under a strong perpendicular magnetic field in periodically modulated fields exhibits a peculiar discrete spectrum near the bottom of the spin-exciton band. The combined effect of the electrostatic modulation potential, and the e-h Coulomb attraction under the magnetic field, leads to nearly bound relative e-h oscillations perpendicular to the modulation axis, which have a characteristic Rydberg-like spectrum near the edge of the spin-exciton band. This low-lying, very narrow excitonic lines may significantly affect the spin and the charge transport in the thermally activated regime.
[show abstract][hide abstract] ABSTRACT: Recent developments in the theory of hyperfine interaction between the nuclear spins and the spins of two dimensional electrons under strong magnetic field and its relevance to the rapidly growing experimental activity in this field is discussed. The crucial role of electron correlations on the nuclear spin-lattice relaxation time and on nuclear spin diffusion is described in the formalism where the elementary excitations are the spin-excitons and skyrmions.
Physica Scripta 12/2006; 1996(T66):158. · 1.03 Impact Factor
[show abstract][hide abstract] ABSTRACT: The ambipolar lateral diffusion of photo-induced charge carriers restricted in a plane of a quantum well (QW) under a moderate (non-quantizing) magnetic field is studied theoretically in the framework of the drift-diffusion model. The continuity equation for this case is solved exactly. The analytical expressions for the concentration of photo-induced electrons and the built-in electric field in the practically important cases of uniform and bell-shaped light beams are obtained in a closed form. It is shown that the ambipolar lateral diffusion of photo-induced charge carriers can be suppressed in InGaAs/GaAs QWs by a moderate magnetic field of ~0.5 mT.
[show abstract][hide abstract] ABSTRACT: We present a detailed theory of induced persistent current produced by
hyperfine interaction in mesoscopic rings based on a 2D-electron (hole) gas in
the absence of external magnetic field. The persistent current emerges due to
combined action of the hyperfine interaction of charge carriers with polarized
nuclei, spin-orbit interaction and Berry phase.
Low Temperature Physics 12/2005; · 0.82 Impact Factor
[show abstract][hide abstract] ABSTRACT: We apply a two-level approach to find an analytical expression for the shape of persistent current oscillations in an one-dimensional mesoscopic ring with a fixed number of electrons at low temperatures. The derived formula has a closed form convenient for further calculations. We use it to obtain the temperature dependence of the persistent current amplitude and to study the orbital magnetic phase transitions.
Journal of Computational and Theoretical Nanoscience 08/2005; 2(3):396-400. · 0.67 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present an analytical theory for the de Haas–van Alphen (dHvA) oscillations in layered organic conductors such as κ-(BEDT-TTF)2Cu(NCS)2 which takes into account the magnetic breakdown and the chemical potential oscillations. For this purpose we have generalized our theory for the chemical potential oscillations in layered conductors [ V.M. Gvozdikov, A.G.M. Jansen, D.I. Pesin, I.D. Vagner and P. Wyder Phys. Rev. B 68 155107 (2003)] to the case of an arbitrary electron dispersion within the layers. Such an approach gives a better agreement with an experimental data for κ-(BEDT-TTF)2Cu(NCS)2 salt than that taking account of the magnetic breakdown (MB) only [ V.M. Gvozdikov, Yu.V. Pershin, E. Steep, A.G.M. Jansen and P. Wyder Phys. Rev. B 65 165102 (2002)]. The magnetization oscillation patterns and the peaks in the fast Fourier transforms (FFT’s) are studied in different combinations of the stochastic and coherent MB regimes with and without the chemical potential oscillations. It is shown that that the chemical potential oscillations in the coherent and stochastic MB regimes do not affect the α and β peaks, but change the amplitudes of the higher harmonics and satellites around the β peak. In the FFT spectrum of κ-(BEDT-TTF)2Cu(NCS)2 two satellites are resolved: β−α (the so called “forbidden” peak) and β+α. In the stochastic MB regime all satellites are depressed. In the coherent MB regime with fixed chemical potential they are higher and have equal amplitudes. Only in the coherent MB regime with oscillating chemical potential the “forbidden” peak β−α becomes larger than the satellite β+α and the calculated FFT spectrum conforms with the FFT spectrum of the dHvA signal of κ-(BEDT-TTF)2Cu(NCS)2.
[show abstract][hide abstract] ABSTRACT: It is shown that the collective spin rotation of a single Skyrmion in quantum Hall ferromagnet can be regarded as precession of the entire spin texture in the external magnetic field, with an effective moment of inertia which becomes infinite in the zero g-factor limit. This low-lying spin excitation may dramatically enhance the nuclear spin relaxation rate via the hyperfine interaction in the quantum well slightly away from filling factor equal one. Comment: 4 pages
[show abstract][hide abstract] ABSTRACT: A coherent superposition of many nuclear spin states can be prepared and manipulated via the hyperfine interaction with the electronic spins by varying the Landau level filling factor through the gate voltage in appropriately designed Quantum Hall Ferromagnet. During the manipulation periods the 2D electron system forms spatially large Skyrmionic spin textures, where many nuclear spins follow locally the electron spin polarization. It is shown that the collective spin rotation of a single spin texture is gapless in the limit of zero Zeeman splitting, and may dominate the nuclear spins relaxation and decoherence processes in the quantum well.
[show abstract][hide abstract] ABSTRACT: This review is devoted to an exposition of the principles of the physics of magnetic domains in non-ferromagnetic metals and diamagnetic phase transitions, which lead to the formation of the so-called Condon domains during magnetic oscillations in a three-dimensional electron gas. One of the goals of the review is to provide a deeper insight into the nature of this instability of the electron gas in normal metals and improve the understanding of this type of non-spin magnetism. We discuss theoretical aspects of the physics underlying magnetic ordering of conduction electrons in bulk metals and in thin films, and describe the behaviour of the susceptibility, thermal expansion, specific heat, compressibility, sound velocity, magnetic induction bifurcation, the order parameter, domain formation, wetting of domain walls, nucleation and kinetics of diamagnetic phase transitions. In the vicinity of diamagnetic phase transitions the results obtained coincide with those following from the Landau theory of phase transitions. The existence of the critical sample size for the diamagnetic phase transition in thin films is considered. We place special emphasis on the problem of the order of diamagnetic phase transitions. The survey is partly motivated as complementary to the recent review by G. Solt and V. Egorov describing the experimental situation in the field.
Advances in Physics, v.52, 385-454 (2003). 01/2003;
[show abstract][hide abstract] ABSTRACT: A theory is presented for the chemical potential oscillations in superlattices in a quantizing magnetic field applied perpendicular to the layers which takes into account the electronic miniband structure attached to each Landau level. This miniband structure in the occupation below the Fermi energy reduces the amplitude of the chemical potential oscillations through a specific integral factor which depends on the density of states related to the electronic motion across the layers.
[show abstract][hide abstract] ABSTRACT: A theoretical study of the indirect coupling of nuclear spins (qubits) embedded in a mesoscopic ring and in a finite-length quantum wire in a magnetic field is presented. It is found that the hyperfine interaction, via the conduction electrons, between nuclear spins exhibits sharp maxima as a function of the magnetic field and nuclear spin positions. This phenomenon can be used for manipulation of qubits with almost atomic precision. Experimental feasibility and implications for quantum logic devices is discussed.
Journal of Physics Condensed Matter 01/2003; · 2.36 Impact Factor
[show abstract][hide abstract] ABSTRACT: We analyze spin effects in the current-carrying state of a superconductor–two-dimensional–electron gas– superconductor S-2DEG-S device with spin-polarized nuclei in the 2DEG region. The hyperfine interaction of 2D electrons with nuclear spins, described by the effective magnetic field B, produces Zeeman splitting of Andreev levels without orbital effects, which leads to an interference pattern of supercurrent oscillations over B. The spin-orbit effects in 2DEG cause a strongly anisotropic dependence of the Josephson current on the direction of B, which may be used as a probe for the spin-orbit interaction intensity. Under certain conditions, the system reveals the properties of junctions. The spin-orbit SO and hyperfine HF interactions in GaAs heterojunctions and similar two-dimensional 2D quantum Hall systems have attracted permanent theoretical and experimental attention. The hyperfine field of the nuclear spin subsystem acting upon the spins of charge carriers may reach 10 4 G. 1 At low temperatures, the nuclear spin relax-ation time can be macroscopically long, 2 so the nonequilib-rium spin population in heterojunctions, once created, is con-served during hundreds of seconds. 3 Zeeman splitting combined with a strong spin-orbit coupling in GaAs/AlGaAs 2DEG gives rise to a novel class of coherent phenomena, e.g., the spontaneous Aharonov-Bohm effect. 4 In this paper we discuss mesoscopic spin-orbit effects in Josephson current flowing across the superconductor-2D-electro-gas–superconductor S-2DEG-S structure Fig. 1 with polarized nuclei in the 2DEG region. The transfer of the Josephson current through the normal conducting layer is provided by the Andreev reflection of electrons and holes at the normal-metal–superconductor NS interfaces, which convert normal electron excitations into Cooper pairs in the superconducting banks. In a pure system with length d smaller than the electron scattering length, the interference between coherent electron states and retro-reflected hole states produces the set of spin-degenerate Andreev energy levels E (), which depend on the quantum numbers and on the difference of the order parameter phases in super-conducting electrodes. 6 In short structures d 0 (0 is the coherence length in the superconductor, the Josephson cur-rent can be presented as the sum of currents transferred by individual Andreev bound states see, e.g., Ref. 7 and refer-ences therein, I 2e
Physical Review B 08/2002; 66(5):052508. · 3.77 Impact Factor
[show abstract][hide abstract] ABSTRACT: The damping of the de Haas–van Alphen (dHvA) oscillations in the mixed state of a 2D superconductor is studied within a new analytical approach to the problem of vortex-lattice fluctuations at high magnetic fields. It is shown that in the ‘liquid’ state around mean field Hc2(T), averaging over phase fluctuations leads to damping of the dHvA osillations, which can be well described by the random vortex lattice model. The calculated damping rate is in a good quantitative agreement with recent experiments carried out on a quasi-2D organic superconductor. It is predicted that deep in the mixed state, the freezing into an ordered vortex lattice is accompanied by a sharp upward turn in the slope of the ‘Dingle plot’.
[show abstract][hide abstract] ABSTRACT: We analyze new spin effects in current-carrying state of superconductor-2D
electron gas-superconductor (S-2DEG-S) device with spin-polarized nuclei in
2DEG region. The hyperfine interaction of 2D electrons with nuclear spins,
described by the effective magnetic field B, produces Zeeman splitting of
Andreev levels without orbital effects, that leads to the interference pattern
of supercurrent oscillations over B. The spin-orbit effects in 2DEG cause
strongly anisotropic dependence of the Josephson current on the direction of B,
which may be used as a probe for the spin-orbit interaction intensity. Under
certain conditions, the system reveals the properties of pi-junction.
[show abstract][hide abstract] ABSTRACT: We present a theoretical study of the influence of the nuclear ferromagnetism on superconductivity in the presence of the electron-nuclear spin interaction. It is demonstrated that in some metals, e.g. Rh, W, the BCS condensate imbedded in a matrix of ferromagneticaly ordered nuclear spins should manifest the FFLO (Fulde-Ferel-Larkin-Ovchinniov) state. We outline that the optimal experimental conditions for observation of FFLO could be achieved by creation, via adiabatic nuclear demagnetization, of the negative nuclear spin temperatures. In this case the nuclear polarization points in the opposite to the external magnetic field direction and the electromagnetic part of the nuclear spin magnetization compensates the external magnetic field, while the exchange part creates the nonhomogeneous superconducting order parameter.
[show abstract][hide abstract] ABSTRACT: The formation of breakdown pattern on an insulating surface under the influence of a transverse magnetic field is theoretically investigated. We, have generalized the Dielectric Breakdown Model (DBM) and random walker model for the case of external magnetic field. It is shown that fractal dimensionality of the discharge saturates with magnetic fields. It is conjectured that nonlinear current interaction is responsible for the experimentally observed "spider-legs" like streamer patterns.
Journal of Statistical Physics 01/2002; · 1.40 Impact Factor
[show abstract][hide abstract] ABSTRACT: The damping of the de Haas-van Alphen (dHvA) oscillations in the mixed state of a 2D superconductor is studied within a new analytical approach to the problem of vortex-lattice fluctuations at high magnetic fields. It is shown that in the 'liquid' state around mean field H-e2(T), averaging over phase fluctuations leads to damping of the dHvA osillations, which can be well described by the random vortex lattice model. The calculated damping rate is in a good quantitative agreement with recent experiments carried out on a quasi-2D organic superconductor. It is predicted that deep in the mixed state, the freezing into an ordered vortex lattice is accompanied by a sharp upward turn in the slope of the 'Dingle plot'. (C) 2002 Elsevier Science B.V. All rights reserved.
[show abstract][hide abstract] ABSTRACT: The energy spectrum of an electron confined to an arbitrary surface of revolution in an external magnetic field, parallel to the symmetry axis, is studied analytically and numerically. Via conformation mapping of the cross section of the circle, the problem is reduced to one on the surface of the sphere. The case of a spheroid is considered in details, and the dependence on parameters is discussed. In the high magnetic field limit a regular structure in the energy spectrum, resembling the Landau levels, is obtained.
[show abstract][hide abstract] ABSTRACT: Electron transport in a new low-dimensional structure - the nuclear spin polarization induced quantum wire (NSPI QW) is theoretically studied. In the proposed system the local nuclear spin polarization creates the effective hyperfine field which confines the electrons with the spins opposite to the hyperfine field to the regions of maximal nuclear spin polarization. The influence of the nuclear spin relaxation and diffusion on the electron energy spectrum and on the conductance of the quantum wire is calculated and the experimental feasibility is discussed. Comment: 5 pages, 4 figures
[show abstract][hide abstract] ABSTRACT: Quantitative theory of the effect of nuclear ferromagnetism on the superconductivity of metals is proposed taking into account
the electron-nuclear spin-spin interactions. At negative nuclear temperatures, when the nuclear magnetization is in opposition
to an external magnetic field, nuclear ferromagnetism is favorable to superconductivity rather than suppressing it. The critical
magnetic field in Be and TiH2.07 hydrate metals may exceed the critical field of a nonmagnetic superconductor by an order of magnitude.