arXiv subjects

Andrei D. Zaikin

Publications and source records attributed to Andrei D. Zaikin.

At least 91 records · Page 5Linked to original sources

arXiv2001

Coulomb Blockade and Insulator-to-Metal Quantum Phase Transition

We analyze an interplay between Coulomb blockade and quantum fluctuations in a coherent conductor (with dimensionless conductance $g \gtrsim 1$) attached to an Ohmic shunt. We demonstrate that at T=0 the system can be either an insulator or a metal depending on whether its total resistance is larger or smaller than $h/e^2\approx 25.8$ k$Ω$. In a metallic phase the Coulomb gap is fully suppressed by quantum fluctuations. We briefly discuss possible relation of this effect to recent experiments indicating the presence of a metal-insulator phase transition in 2d disordered systems.

cond-mat.mes-hall↗

arXiv2001

Comparison between Theory and Some Recent Experiments on Quantum Dephasing

We report on a quantitative comparison between our theory of quantum dephasing at low temperatures and some recent experimental results [D. Natelson {\it et al.}, Phys. Rev. Lett. {\bf 86}, 1821 (2001); A.B. Gougam {\it et al.}, J. Low Temp. Phys. {\bf 118}, 447 (2000); F. Pierre {\it et al.} cond-mat/0012038].

cond-mat.mes-hall↗

arXiv2000

Quantum Tunneling of the Order Parameter in Superconducting Nanowires

Quantum tunneling of the superconducting order parameter gives rise to the phase slippage process which controls the resistance of ultra-thin superconducting wires at sufficiently low temperatures. If the quantum phase slip rate is high, superconductivity is completely destroyed by quantum fluctuations and the wire resistance never decreases below its normal state value. We present a detailed microscopic theory of quantum phase slips in homogeneous superconducting nanowires. Focusing our attention on relatively short wires we evaluate the quantum tunneling rate for phase slips, both the quasiclassical exponent and the pre-exponential factor. In very thin and dirty metallic wires the effect is shown to be clearly observable even at $T \to 0$. Our results are fully consistent with recent experimental findings [A. Bezryadin, C.N. Lau, and M. Tinkham, Nature {\bf 404}, 971 (2000)] which provide direct evidence for the effect of quantum phase slips.

cond-mat.mes-hall↗

arXiv2000

Coulomb Interaction and Quantum Transport through a Coherent Scatterer

An interplay between charge discreteness, coherent scattering and Coulomb interaction yields nontrivial effects in quantum transport. We derive a real time effective action and an equivalent quantum Langevin equation for an arbitrary coherent scatterer and evaluate its current-voltage characteristics in the presence of interactions. Within our model, at large conductances $G_0$ and low $T$ (but outside the instanton-dominated regime) the interaction correction to $G_0$ saturates and causes conductance suppression by a universal factor which depends only on the type of the conductor.

cond-mat.mes-hall↗

arXiv2000

Tunneling through an Anderson impurity between superconductors

We consider an Anderson impurity (A) weakly connected to a superconducting electrode (S) on one side and a superconducting or a normal metal electrode (N) on the other side. A general path integral formalism is developed and the response of SAN and SAS junctions to a constant voltage bias V is elucidated, using a combination of the Keldysh technique (to handle non-equilibrium effects) and a dynamical mean field approximation (to handle repulsive Hubbard interactions). An interesting physics is exposed at sub-gap voltages ($eV < Δ$ for SAN and $eV < 2 Δ$ for SAS). For an SAN junction, Andreev reflection is strongly affected by Coulomb interaction. For superconductors with p-wave symmetry the junction conductance exhibits a remarkable peak at $eV < Δ$, while for superconductors with s-wave symmetric pair potential the peak is shifted towards the gap edge $eV=Δ$ and strongly suppressed if the Hubbard repulsive interaction increases.Electron transport in SAS junctions is determined by an interplay between multiple Andreev reflection (MAR) and Coulomb effects. For s-wave superconductors the usual peaks in the conductance that originate from MAR are shifted by interaction to larger values of V. They are also suppressed as the Hubbard interaction strength grows. For p-wave superconductors the sub-gap current is much larger and the I-V characteristics reveal a new feature, namely, a peak in the current resulting from a mid-gap bound state in the junction.

cond-mat.str-el↗

arXiv2000

Quantum Dot between two Superconductors

Novel effects emerge from an interplay between multiple Andreev reflections and Coulomb interaction in quantum dot coupled to superconducting leads and subject to a finite potential bias $V$. Combining an intuitive physical picture with rigorous path integral formalism we evaluate the current $I$ through the dot and find that the interaction shifts the subharmonic pattern of the $I-V$ curve is shifted toward higher $V$. For sufficiently ^M strong interaction the subgap current (at $eV < 2 Δ$) is virtually suppressed.

cond-mat.str-el↗

arXiv1999

Quasiclassical Green's function approach to mesoscopic superconductivity

Recent experiments on mesoscopic normal-metal--superconductor heterostructures resolve properties on length scales and at low temperatures such that the temperature is below the Thouless energy $k_B T \le E_{Th}$. We describe the properties of these systems within the framework of quasiclassical many-body techniques. Diffusive and ballistic systems are covered, both in equilibrium and nonequilibrium situations. Thereby we demonstrate the common physical basis of various subtopics.

cond-mat.mes-hall↗

arXiv1998

Reply to a Comment on "Quantum Decoherence in Disordered Mesoscopic Systems" (cond-mat/9808078, cond-mat/9808053)

We reply to the critique of our results raised by Aleiner, Altshuler and Gershenzon (AAG) in cond-mat/9808078 and cond-mat/9808053. We demonstrate that our path integral analysis fully reproduces the results of AAG if analyzed on a perturbative level. This should settle the issue of "missing diagrams" in our calculation. We, furthermore, demonstrate that our approach allows us to proceed beyond the Golden-rule-type perturbation theory employed by AAG. This explains the difference between our and AAG's results. We also comment on the comparison of our results with the experiments presented by AAG.

cond-mat↗

arXiv1998

Comment on ``On loss of quantum coherence in an interacting Fermi gas'' (cond-mat/9810297)

In a recent paper \cite{EH} Eriksen and Hedegard (EH) claimed that they ``clarified'' our path integral calculation \cite{GZ1} and found an error in our analysis. Here we will demonstrate that this claim is based on mathematically incorrect and physically meaningless procedure invented by the authors \cite{EH}. The main problem in the EH analysis is due to their erroneous calculation of Gaussian path integrals and has nothing to do with the momentum recoil of a particle interacting with an external bath.

cond-mat↗

arXiv1998

Strong Charge Fluctuations in the Single-Electron Box: A Quantum Monte Carlo Analysis

We study strong electron tunneling in the single-electron box, a small metallic island coupled to an electrode by a tunnel junction, by means of quantum Monte Carlo simulations. We obtain results, at arbitrary tunneling strength, for the free energy of this system and the average charge on the island as a function of an external bias voltage. In much of the parameter range an extrapolation to the ground state is possible. Our results for the effective charging energy for strong tunneling are compared to earlier -- in part controversial -- theoretical predictions and Monte Carlo simulations.

cond-mat.mes-hall↗

arXiv1998

The Mesoscopic SNS Transistor

In a mesoscopic superconductor - normal metal - superconductor (SNS) heterostructure the quasiparticle distribution can be driven far from equilibrium by a voltage applied across the normal metal. This reduces the supercurrent between the superconducting electrodes, which creates the possibility to use these SNS junctions as fast switches and transistors. We describe the system in the framework of the quasiclassical theory and find good agreement with recent experiments. We propose further experimental tests, for instance the voltage-dependence of the current-phase-relation, which includes a transition to a $π$-junction.

cond-mat.supr-con↗

arXiv1997

Quantum Decoherence and Weak Localization at Low Temperatures

We develope a theory of a fundamental effect of the interaction-induced decoherence of the electron wave function in a disordered metal. With the aid of the Keldysh technique and the path integral formalism we derive a formally exact equation of motion for the electron density matrix in the presence of interaction. We demonstrate that the effect of interaction of the electron with other electrons and lattice ions in a disordered metal is equivalent to that of an effective dissipative environment. Quantum noise of this environment causes quantum decoherence even at T=0. Our analysis explicitely accounts for the Pauli principle which plays an important role for inelastic scattering processes but turns out not to affect quantum decoherence. Our results seriously challenge the existence of strong localization in low dimensional disordered metals.

cond-mat↗

arXiv1997

Quantum Decoherence in Disordered Mesoscopic Systems

We point out that the low temperature saturation of the electron phase decoherence time in a disordered conductor can be explained within the existing theory of weak localization provided the effect of quantum (high frequency) fluctuations is taken into account. Making use of the fluctuation-dissipation theorem we evaluate the quantum decoherence time, the crossover temperature below which thermal effects become unimportant, and the weak localization correction $δσ$ at T=0. For 1d systems the latter is found to be $δσ\propto 1/ \sqrt{N}$, where $N$ is the number of conducting channels.

cond-mat↗

arXiv1997

Coherent Electron Transport in Superconducting-Normal Metallic Films

We study the transport properties of a quasi-two-dimensional diffusive normal metal film attached to a superconductor. We demonstrate that the properties of such films can essentially differ from those of quasi-one-dimensional systems: in the presence of the proximity induced superconductivity in a sufficiently wide film its conductance may not only increase but also decrease with temperature. We develop a quantitative theory and discuss the physical nature of this effect. Our theory provides a natural explanation for recent experimental findings referred to as the ``anomalous proximity effect''.

cond-mat.supr-con↗

arXiv1997

Reply to the Comment on 'Quantum Phase Slips and Transport in Ultra-Thin Superconducting Wires'

We reply to the recent Comment [cond-mat/9702231] by J.-M. Duan. Our point of view is markedly different on every issue raised. Much of the disagreement can be traced to a different preception of experimentally relevant length scales. i) We explain the difference between our formulation, which rests on a microscopic basis, and the phenomenological one of the author. ii) Our renormalization scheme is fundamentally right, as the "log(log)" interaction appears only in wires of astronomical lengths. iii) The tunneling barrier is profoundly reduced by the kinetic inductance. iv) We do make an appropriate comparison to the data on the thinnest available wires.

cond-mat.supr-con↗

arXiv1997

Dynamics and Effective Actions of BCS Superconductors

We derive effective dynamical theories for metals and BCS superconductors, based on the effective action formalism. Both the metallic regime $T\gtrsim T_{C}$ and the superconducting regime $T\ll T_{C}$ are studied in the clean and dirty limit. Furthermore, we consider the effect of particle-hole asymmetry in the band structure. Using gauge invariance, the electrodynamics of the problem is formulated in a transparent way. The effective actions are useful starting points for treating dynamical problems involving BCS superconductors.

cond-mat.supr-con↗

arXiv1996

Quantum Fluctuations and Resistivity of Thin Superconducting Wires

We present a microscopic study of the quantum fluctuations of the superconducting order parameter in thin homogeneous superconducting wires at all temperatures below $T_C$. The rate of quantum phase slip processes determines the resistance $R(T)$ of the wire, which is observable in very thin wires, even at low temperature. Furthermore, we predict a new low temperature metallic phase below a critical wire-thickness in the 10nm range, in which quantum phase slips proliferate.

cond-mat↗

arXiv1996

Supercurrent in a mesoscopic proximity wire

Recent experiments on the proximity induced supercurrent in mesoscopic normal wires revealed a surprising temperature dependence. They suggest clean-limit behavior although the wires are strongly disordered. We demonstrate that this unexpected scaling is actually contained in the conventional description of diffusive superconductors and find excellent agreement with the experimental results. In addition we propose a SQUID-like proximity structure for further experimental investigations of the effects in question.

cond-mat↗