Publications (192)449.07 Total impact
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ABSTRACT: The Kondo effect in a quantum dot is discussed. In the standard Coulomb blockade setting, tunneling between the dot and the leads is weak, the number of electrons in the dot is welldefined and discrete; the Kondo effect may be considered in the framework of the conventional onelevel Anderson impurity model. It turns out however, that the Kondo temperature TK in the case of weak tunneling is extremely low. In the opposite case of almost reflectionless singlemode junctions connecting the dot to the leads, the average charge of the dot is not discrete. Surprisingly, its spin may remain quantized: s=1/2 or s=0, depending (periodically) on the gate voltage. Such a "spincharge separation" occurs because, unlike an Anderson impurity, a quantum dot carries a broadband, dense spectrum of discrete levels. In the doublet state, the Kondo effect develops with a significantly enhanced TK. Like in the weaktunneling regime, the enhanced TK exhibits strong mesoscopic fluctuations. The statistics of the fluctuations is universal, and related to the PorterThomas statistics of the wave function fluctuations.International Journal of Modern Physics B 01/2012; 15(10n11). DOI:10.1142/S0217979201005921 · 0.94 Impact Factor  Physical Review B 08/2007; 76(6). DOI:10.1103/PhysRevB.76.069902 · 3.74 Impact Factor
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ABSTRACT: Local vortex dynamics in Bi2Sr2CaCu2O8 single crystals was studied using novel microscopic GaAs/AlGaAs Hallsensor arrays. The irreversibility line (IL) is found to exist in the absence of bulk pinning. At high temperatures the IL is due to geometrical barriers whereas at intermediate temperatures the irreversible behavior is determined by surface barriers. Bulk pinning governs the IL only at T < 22 K.EPL (Europhysics Letters) 07/2007; 30(6):367. DOI:10.1209/02955075/30/6/009 · 2.27 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the energy and phase relaxation of a superconducting qubit caused by a single quasiparticle. In our model, the qubit is an isolated system consisting of a small island (Cooperpair box) and a larger superconductor (reservoir) connected with each other by a tunable Josephson junction. If such system contains an odd number of electrons, then even at lowest temperatures a single quasiparticle is present in the qubit. Tunneling of a quasiparticle between the reservoir and the Cooperpair box results in the relaxation of the qubit. We derive master equations governing the evolution of the qubit coherences and populations. We find that the kinetics of the qubit can be characterized by two time scales  quasiparticle escape time from reservoir to the box, $\Gamma^{1}_{in}$, and quasiparticle relaxation time $\tau$. The former is determined by the dimensionless normalstate conductance $g_T$ of the Josephson junction and oneelectron level spacing $\delta_r$ in the reservoir ($\Gamma_{in}\sim g_T\delta_r$), and the latter is due to electronphonon interaction. We find that phase coherence is damped on the time scale of $\Gamma^{1}_{in}$. The qubit energy relaxation depends on the ratio of the two characteristic times, $\tau$ and $\Gamma^{1}_{in}$, and also on the ratio of temperature $T$ to the Josephson energy $E_J$.Physical Review B 06/2007; 75(22). DOI:10.1103/PhysRevB.75.229903 · 3.74 Impact Factor 
Article: Transition from a OneDimensional to a QuasiOneDimensional State in Interacting Quantum Wires
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ABSTRACT: Upon increasing the electron density in a quantum wire, the onedimensional electron system undergoes a transition to a quasionedimensional state. In the absence of interactions between electrons, this corresponds to filling up the second subband of transverse quantization, and there are two gapless excitation modes above the transition. On the other hand, strongly interacting onedimensional electrons form a Wigner crystal, and the transition corresponds to it splitting into two chains (zigzag crystal). We show that the soft mode driving the transition to the zigzag state is gapped, and only one gapless mode exists above the transition. Furthermore, we establish that in the vicinity of the transition already arbitrarily weak interactions open a gap in the second mode. We then argue that only one gapless mode exists near the transition at any interaction strength.Physical Review Letters 04/2007; 98(12):126404. DOI:10.1103/PhysRevLett.98.126404 · 7.51 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the energy and phase relaxation of a superconducting qubit caused by a single quasiparticle. In our model, the qubit is an isolated system consisting of a small island (Cooperpair box) and a larger superconductor (reservoir) connected with each other by a tunable Josephson junction. If such a system contains an odd number of electrons, then even at lowest temperatures a single quasiparticle is present in the qubit. Tunneling of a quasiparticle between the reservoir and the Cooperpair box results in the relaxation of the qubit. We derive master equations governing the evolution of the qubit coherences and populations. We find that the kinetics of the qubit can be characterized by two time scales—quasiparticle escape time from the reservoir to the box Γin1 and quasiparticle relaxation time τ . The former is determined by the dimensionless normalstate conductance gT of the Josephson junction and oneelectron level spacing δr in the reservoir (Γin˜gTδr) , and the latter is due to the electronphonon interaction. We find that phase coherence is damped on the time scale of Γin1 . The qubit energy relaxation depends on the ratio of the two characteristic times τ and Γin1 and also on the ratio of temperature T to the Josephson energy EJ .Physical review. B, Condensed matter 08/2006; 74(6):64515. DOI:10.1103/PhysRevB.74.064515 · 3.66 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We review a novel approach to the superconductive proximity effect in disordered normalsuperconducting (NS) structures. The method is based on the multicharge Keldysh action and is suitable for the treatment of interaction and fluctuation effects. As an application of the formalism, we study the subgap conductance and noise in twodimensional NS systems in the presence of the electronelectron interaction in the Cooper channel. It is shown that singular nature of the interaction correction at large scales leads to a nonmonotonuos temperature, voltage and magnetic field dependence of the Andreev conductance.Pramana 06/2005; 64(6):10391049. DOI:10.1007/BF02704166 · 0.72 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We analyze the decay of Rabi oscillations in a charge qubit consisting of a Cooper pair box connected to a finitesize superconductor by a Josephson junction. We concentrate on the contribution of quasiparticles in the superconductors to the decay rate. Passing of a quasiparticle through the Josephson junction tunes the qubit away from the charge degeneracy, thus spoiling the Rabi oscillations. We find the temperature dependence of the quasiparticle contribution to the decay rate for open and isolated systems. The former case is realized if a normalstate trap is included in the circuit, or if just one vortex resides in the qubit; the decay rate has an activational temperature dependence with the activation energy equal to the superconducting gap $\Delta$. In a superconducting qubit isolated from the environment, the activation energy equals $2\Delta$ if the number of electrons is even, while for an odd number of electrons the decay rate of an excited qubit state remains finite in the limit of zero temperature. We estimate the decay rate for realistic parameters of a qubit.Physical review. B, Condensed matter 04/2005; 72(1). DOI:10.1103/PhysRevB.72.014517 · 3.66 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We consider a class of systems where, due to the large mismatch of dielectric constants, the Coulomb interaction is approximately onedimensional. Examples include ion channels in lipid membranes and water filled nanopores in silicon or cellulose acetate films. Charge transport across such systems possesses the activation behavior associated with the large electrostatic selfenergy of a charge placed inside the channel. We show here that the activation barrier exhibits nontrivial dependence on the salt concentration in the surrounding water solution and on the length and radius of the channel.Physica A: Statistical Mechanics and its Applications 04/2005; DOI:10.1016/j.physa.2005.05.097 · 1.72 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The temperature dependence of electron dephasing time tau(phi)(T) is calculated for a disordered metal with a small concentration of superconductive grains. Above the macroscopic superconducting transition line, when electrons in the metal are normal, Andreev reflection from the grains leads to a nearly temperatureindependent contribution to the dephasing rate. In a broad temperature range tau(1)(phi)(T) strongly exceeds the prediction of the classical theory of dephasing in normal disordered conductors, whereas magnetoresistance is dominated (in two dimensions) by the MakiTompson correction and is positive.Physical Review Letters 07/2004; 92(24):247002. DOI:10.1007/1402021933_3 · 7.51 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We consider the classicalquantum behavior crossover in a small, externally driven Josephson junction. Charge of a small superconducting grain fluctuates strongly if its critical current J_c(t) is modulated (kicked) by short periodic pulses (e.g. by changing the tunneling strength). The system may be mapped onto the model of quantum kicked rotator [1]. For large amplitudes of J_c(t) and short enough times, the grain charge, Q(t), diffuses in time. That is, the charge correlation function K(t) = <(Q(t)Q(0))^2> = 2Dt, where the classical diffusion coefficient, D, may be expressed through the microscopical parameters of the model. Quantum corrections develop at times longer than the Ehrenfest time of the corresponding dynamical system, t_E ˜ ln D/(2e)^2. We have calculated weaklocalization oneloop renormalization of the diffusion coefficient, δ D(ω), and found δ K(t)= 4/3√ π 2e√ D (t2t_E)^3/2 for 2tE ˜ t≪ t_L, where t_L ˜ D/(2e)^2 is the time to develop the strong localization [1,2]. The predicted classicalquantum crossover may be observed by performing timeresolved potentiometry on the kicked Josephson grain. Alternatively, the effect may be detected by driving a periodic current of a large amplitude, J≫ J_c, across the grain and monitoring fluctuations of voltage. We believe that such a crossover applies to other periodic driven systems. [1] G. Casati et. al., Lect. Notes Phys.93, 334 (1979). [2] S.Fishman et. al. Phys. Rev. Lett. 49, 509 (1982); A.Altland, ibid. 71, 69 (1993).  [Show abstract] [Hide abstract]
ABSTRACT: We study a crossover from classical to quantum picture in the electron energy statistics in a system with broken timereversal symmetry. The perturbative and nonperturbative parts of the two level correlation function, $R(\omega)$ are analyzed. We find that in the intermediate region, $\Delta\ll\omega\sim t_E^{1}\ll t_{erg}^{1}$, where $t_E$ and $t_{erg}$ are the Ehrenfest and ergodic times, respectively, $R(\omega)$ consists of a series of oscillations with the periods depending on $t_E$, deviating from the universal WignerDyson statistics. These Ehrenfest oscillations have the period dependence as $t_E^{1}$ in the perturbative part. [For systems with timereversal symmetry, this oscillation in the perturbative part of $R(\omega)$ was studied in an earlier work (I. L. Aleiner and A. I. Larkin, Phys. Rev. E {\bf 55}, R1243 (1997))]. In the nonperturbative part they have the period dependence as $(\Delta^{1}+\alpha t_E)^{1}$ with $\alpha$ a universal numerical factor. The amplitude of the leading order Ehrenfest oscillation in the nonperturbative part is larger than that of the perturbative part. Comment: 20 pages, 4 figures, submitted to Phys. Rev. BPhysical Review B 10/2003; 70(3). DOI:10.1103/PhysRevB.70.035305 · 3.74 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We consider the effect of the RKKY interaction between magnetic impurities on the electron relaxation rates in a normal metal. The interplay between the RKKY interaction and the Kondo effect may result in a nonmonotonic temperature dependence of the electron momentum relaxation rate, which determines the Drude conductivity. The electron phase relaxation rate, which determines the magnitude of the weak localization correction to the resistivity, is also a nonmonotonic function of temperature. For this function, we find the dependence of the position of its maximum on the concentration of magnetic impurities. We also relate the electron energy relaxation rate to the excitation spectrum of the system of magnetic impurities. The energy relaxation determines the distribution function for the outofequilibrium electrons. Measurement of the electron distribution function thus may provide information about the excitations in the spin glass phase. Comment: 15 pages, 5 figuresPhysical review. B, Condensed matter 05/2003; 68(7). DOI:10.1103/PhysRevB.68.075119 · 3.66 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Without AbstractJETP Letters 01/2003; 77(2):118118. DOI:10.1134/1.1564233 · 1.36 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: What quantity controls the Coulomb blockade oscillations if the dotlead conductance is essentially frequency dependent? We argue that it is the conductance at the imaginary frequency given by the effective charging energy. The latter may be very different from the bare charging energy due to the interfaceinduced capacitance (or inductance). These observations are supported by a number of examples, considered from the weak and strong coupling (perturbation theory versus instanton calculus) perspectives.Physical Review Letters 01/2003; 89(23):236801. DOI:10.1103/PhysRevLett.89.236801 · 7.51 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the crossover from the semiclassical to the quantum description of electron energy states in a chaotic metal grain connected to a superconductor. We consider the influence of scattering off point impurities (quantum disorder) and of quantum diffraction (quantum chaos) on the electron density of states. We show that both the quantum disorder and the quantum chaos open a gap near the Fermi energy. The size of the gap is determined by the mean free time in disordered systems and by the Ehrenfest time in clean chaotic systems. Particularly, if both times become infinitely large, the density of states is gapless, and if either of these times becomes shorter than the electron escape time, the density of states is described by random matrix theory. Using the Usadel equation, we also study the density of states in a grain connected to a superconductor by a diffusive contact. Comment: 20 pages, 10 figuresPhysical review. B, Condensed matter 10/2002; 67(11). DOI:10.1103/PhysRevB.67.115335 · 3.66 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The superconductivity in very thin rings is suppressed by quantum phase slips. As a result, the amplitude of the persistent current oscillations with flux becomes exponentially small, and their shape changes from sawtooth to a sinusoidal one. We reduce the problem of lowenergy properties of a superconducting nanoring to that of a quantum particle in a sinusoidal potential and show that the dependence of the current on the flux belongs to a oneparameter family of functions obtained by solving the respective Schrödinger equation with twisted boundary conditions.Physical Review Letters 09/2002; 89(9):096802. DOI:10.1103/PhysRevLett.89.096802 · 7.51 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: It is shown that states with phase increments deltaphi > pi can form in superconductornarrowing (normal metal)superconductor systems. If the conditions a << l << xi(0), where a is the crosssectional size of the narrowing, l is the length of narrowing, and xi(0) is the correlation radius at zero temperature, are satisfied, there is a region of parameters (a, l, xi(0), T) in which the critical current is attained in solutions with a phase difference deltaphi > pi. (C) 2002 MAIK "Nauka / Interperiodica".JETP Letters 09/2002; DOI:10.1134/1.1520631 · 1.36 Impact Factor 
Article: Spin glass versus superconductivity
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ABSTRACT: A superconductor with interacting paramagnetic impurities is considered. The impurities are coupled via the RudermanKittelKasuyaYosida (RKKY) interaction. At a temperature Tg, the system of magnetic impurities forms a spinglass state. We study the effect of the spinspin interactions on the superconducting transition point at T<Tg. We show that superconducting properties depend on the state of the spin system via spinspin autocorrelation functions. With the help of the Keldysh technique, a general nonequilibrium Gor’kov equation is derived. Possible aging effects in the superconducting transition point are discussed. The equilibrium superconducting transition point is found explicitly and shown to be shifted towards higher temperatures and impurity concentrations compared to the classical AbrikosovGor’kov curve. The corresponding shift of the superconducting quantum critical point is quite small (about 10%). A method of calculating spinspin correlation function is suggested. The method combines the ideas of random meanfield method and virial expansion. We calculate analytically the first virial term for the spinspin correlator for the quantum Heisenberg spin glass with the RKKY interactions in the quasiequilibrium regime.Physical Review B 08/2002; 66(6). DOI:10.1103/PhysRevB.66.064526 · 3.74 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The leading (Gaussian) fluctuation correction to the weak coupling zero temperature BCS superconducting gap equation is computed. We find that the dominant contribution comes from the high energies and momenta (compared to the gap) and gives a correction smaller by the weakcoupling factor $gN_0$ than the meanfield terms. This correction is small due to cancellation of singular contributions from the amplitude and phase mode at high energies and momenta.Physical Review B 08/2002; 70(21). DOI:10.1103/PhysRevB.70.214531 · 3.74 Impact Factor
Publication Stats
12k  Citations  
449.07  Total Impact Points  
Top Journals
Institutions

1996–2012

University of Minnesota Duluth
 Department of Physics
Duluth, Minnesota, United States


1994–2007

Weizmann Institute of Science
 Department of Physics of Condensed Matter
Tel Aviv, Tel Aviv, Israel 
University of Florence
Florens, Tuscany, Italy 
Bar Ilan University
 Department of Physics
Ramat Gan, Tel Aviv, Israel


1973–2002

Russian Academy of Sciences
 L. D. Landau Institute for Theoretical Physics
Moskva, Moscow, Russia


1999–2000

RuhrUniversität Bochum
 Institut für Theoretische Physik III
Bochum, North RhineWestphalia, Germany


1993–1996

Argonne National Laboratory
 Division of Materials Science
Lemont, Illinois, United States 
University of California, Santa Barbara
Santa Barbara, California, United States 
Rutgers, The State University of New Jersey
 Department of Physics
НьюБрансуик, New Jersey, United States


1980–1996

Institute for Theoretical and Experimental Physics
Moskva, Moscow, Russia


1989–1995

The University of Tokyo
 Department of Applied Life Sciences
Tōkyō, Japan


1992

University of California, Los Angeles
Los Ángeles, California, United States


1988

Abdus Salam International Centre for Theoretical Physics
Trst, Friuli Venezia Giulia, Italy


1962

Kurchatov Institute
Moskva, Moscow, Russia
