arXiv subjects

A. D. Zaikin

Publications and source records attributed to A. D. Zaikin.

At least 37 records · Page 2Linked to original sources

arXiv2004

Transport of interacting electrons in arrays of quantum dots and diffusive wires

We develop a detailed theoretical investigation of the effect of Coulomb interaction on electron transport in arrays of chaotic quantum dots and diffusive metallic wires. Employing the real time path integral technique we formulate a new Langevin-type of approach which exploits a direct relation between shot noise and interaction effects in mesoscopic conductors. With the aid of this approach we establish a general expression for the Fano factor of 1D quantum dot arrays and derive a complete formula for the interaction correction to the current which embraces all perturbative results previously obtained for various quasi-0D and quasi-1D disordered conductors and extends these results to yet unexplored regimes.

cond-mat.mes-hall↗

arXiv2003

Statistics of current fluctuations at non-zero frequencies

We formulate a general approach which describes statistics of current fluctuations in mesoscopic coherent conductors at arbitrary frequencies and in the presence of interactions. Applying this approach to the non-interacting case, we analyze frequency dispersion of the third cumulant of the current operator ${\cal S}_3$ at frequencies well below both the inverse charge relaxation time and the inverse electron dwell time. This dispersion turns out to be important in the frequency range comparable to applied voltages. For comparatively transparent conductors it may lead to the sign change of ${\cal S}_3$

cond-mat.mes-hall↗

arXiv2002

Current Fluctuations and Electron-Electron Interactions in Coherent Conductors

We analyze current fluctuations in mesoscopic coherent conductors in the presence of electron-electron interactions. In a wide range of parameters we obtain explicit universal dependencies of the current noise on temperature, voltage and frequency. We demonstrate that Coulomb interaction decreases the Nyquist noise. In this case the interaction correction to the noise spectrum is governed by the combination $\sum_nT_n(T_n-1)$, where $T_n$ is the transmission of the $n$-th conducting mode. The effect of electron-electron interactions on the shot noise is more complicated. At sufficiently large voltages we recover two different interaction corrections entering with opposite signs. The net result is proportional to $\sum_nT_n(T_n-1)(1-2T_n)$, i.e. Coulomb interaction decreases the shot noise at low transmissions and increases it at high transmissions.

cond-mat.mes-hall↗

arXiv2002

Proximity-induced screening and its magnetic breakdown in mesoscopic hybrid structures

We derive a general microscopic expression for the non-linear diamagnetic current in a clean superconductor-insulator-normal metal structure with an arbitrary interface transmission. In the absence of electron-electron interactions in the normal metal the diamagnetic response increases monotonously with decreasing temperature showing no sign of paramagnetic reentrance down to T=0. We also analyze the magnetic breakdown of proximity induced Meissner screening. We demonstrate that the magnetic breakdown field should be strongly suppressed in the limit of small interface transmissions while the linear diamagnetic current does not depend on the transmission of the insulating barrier at low enough temperatures.

cond-mat.supr-con↗

arXiv2002

Superconductor Quantum Dot Superconductor Junction in the Kondo Regime

Electron transport between two superconductors through an Anderson impurity in the Kondo regime is investigated within the slave boson mean field approximation. The current, shot noise power and Fano factor are displayed versus the applied bias voltage in the subgap region and found to be strongly dependent on the ratio between the Kondo temperature $T_{K}$ and the superconducting gap $Δ$. In particular, the $I-V$ curve exposes an excess current in the limit $T_{K}/Δ\gg 1$.

cond-mat.str-el↗

arXiv2001

On Low-Temperature Dephasing by Electron-Electron Interaction

The quantum coherence of electrons can be probed by studying weak localization corrections to the conductivity. Interaction effects lead to dephasing, with electron-electron interactions being the important intrinsic mechanism. A controversy exists whether or not the dephasing rate, as measured in a weak localization experiment, vanishes at low temperatures. We review the non-perturbative analysis of this question and some of the arguments which have been raised against it. The compact form of the presentation should make the derivation more transparent and accessible for discussions. We also compare with recent experiments.

cond-mat↗

arXiv2001

Coulomb Effects and Electron Transport Through a Coherent Conductor

We analyze electron transport through relatively short coherent conductors in the presence of Coulomb interaction. We evaluate the current-voltage characteristics of such conductors taking into account the effect of an external environment. Within our model, at large conductances and low $T$ the conductance is suppressed by a universal factor which depends only on the type of the conductor. We also argue that at T=0 the system ``scatterer+shunt'' can be either an insulator or a metal depending on whether its total resistance is larger or smaller than $R_Q=h/e^2\approx 25.8$ k$Ω$. In a metallic phase the Coulomb gap is fully suppressed by quantum fluctuations.

cond-mat.mes-hall↗

arXiv2001

The Josephson critical current in a long mesoscopic S-N-S junction

We carry out an extensive experimental and theoretical study of the Josephson effect in S-N-S junctions made of a diffusive normal metal (N) embedded between two superconducting electrodes (S). Our experiments are performed on Nb-Cu-Nb junctions with highly-transparent interfaces. We give the predictions of the quasiclassical theory in various regimes on a precise and quantitative level. We describe the crossover between the short and the long junction regimes and provide the temperature dependence of the critical current using dimensionless units $eR_{N}I_{c}/ε_{c}$ and $k_{B}T/ε_{c}$ where $ε_{c}$ is the Thouless energy. Experimental and theoretical results are in excellent quantitative agreement.

cond-mat.mes-hall↗

arXiv2000

Shot noise in superconducting junctions with weak link formed by Anderson impurity

A theory is developed to study shot noise in superconducting (SAS) and hybrid (SAN) junctions with singly occupied Anderson impurity (A) as a weak link. The zero-frequency DC component of the shot noise spectral density is calculated at zero temperature as a function of the bias at different Coulomb repulsion strengths U, and show a remarkable structure resulting from combination of electron-electron interaction and Andreev reflections.

cond-mat.supr-con↗

arXiv2000

Coulomb blockade in one-dimensional arrays of high conductance tunnel junctions

Properties of one-dimensional (1D) arrays of low Ohmic tunnel junctions (i.e. junctions with resistances comparable to, or less than, the quantum resistance $R_{\rm q}\equiv h/e^2\approx 25.8$ k$Ω$) have been studied experimentally and theoretically. Our experimental data demonstrate that -- in agreement with previous results on single- and double-junction systems -- Coulomb blockade effects survive even in the strong tunneling regime and are still clearly visible for junction resistances as low as 1 k$Ω$. We have developed a quasiclassical theory of electron transport in junction arrays in the strong tunneling regime. Good agreement between the predictions of this theory and the experimental data has been observed. We also show that, due to both heating effects and a relatively large correction to the linear relation between the half-width of the conductance dip around zero bias voltage, $V_{1/2}$, and the measured electronic temperature, such arrays are inferior to those conventionally used in the Coulomb Blockade Thermometry (CBT). Still, the desired correction to the half-width, $ΔV_{1/2}$, can be determined rather easily and it is proportional to the magnitude of the conductance dip around zero bias voltage, $ΔG$. The constant of proportionality is a function of the ratio of the junction and quantum resistances, $R/R_{\rm q}$, and it is a pure strong tunneling effect.

cond-mat.mes-hall↗

arXiv1999

Quantum Fluctuations and Dissipation in Thin Superconducting Wires

We investigate quantum fluctuations in thin superconducting wires. We demonstrate that quantum phase slips dominate the system behavior at low temperatures and are well in the measurable range for sufficiently thin wires. We discuss the effect of dissipation, predict a new quantum superconductor-to-metal (insulator) phase transitions for wires with thicknesses in the 10-nm range, evaluate the resistance R(T) of such wires and compare our results with recent experimental findings.

cond-mat.mes-hall↗

arXiv1999

Interaction and Quantum Decoherence in Disordered Conductors

We present a nonperturbative approach which allows to evaluate the weak localization correction to the conductivity of disordered conductors in the presence of interactions. The effect of the electron-electron interaction on the magnetoconductance is described by the function A(t)\exp (-f(t)). The dephasing time is determined only by f(t), and this time remains finite down to T=0 due to the electron-electron interactions. In order to establish the relation between our nonperturbative analysis and the perturbative results the effect of interaction on the pre-exponent A(t) should be taken into account. The dephasing time cannot be unambiguously determined from a perturbative calculation.

cond-mat.mes-hall↗

arXiv1999

Interactions and Weak Localization: Perturbation Theory and Beyond

We establish an explicit correspondence between perturbative and nonperturbative results in the problem of quantum decoherence in disordered conductors. We demonstrate that the dephasing time $τ_ϕ$ cannot be unambiguously extracted from a perturbative calculation. We show that the effect of the electron-electron interaction on the magnetoconductance is described by the function $A_d(t)\exp (-f_d(t))$. The dephasing time is determined by $f_d(t)$, i.e. in order to evaluate $τ_ϕ$ it is sufficient to perform a nonperturbative analysis with an exponential accuracy. The effect of interaction on the pre-exponent $A_d(t)$ is important if one calculates the interaction-dependent part of the weak localization correction for strong magnetic fields. The zero temperature dephasing time drops out of this correction in the first order due to the exact cancellation of the linear in time $T$-independent contributions from the exponent and the pre-exponent. Nonlinear in time $T$-independent contributions do not cancel out already in the first order of the perturbation theory and yield an additional contribution to dephasing at all temperatures including T=0.

cond-mat.mes-hall↗

arXiv1999

Quantum Decoherence and the "P(E)-Theory"

We point out a close physical and formal similarity between the problems of electron tunneling in the effective environment and the weak localization effects in the presence of interactions. In both cases the results are expressed in terms of the ``energy probability distribution function'' $P(E)$ which has a finite width even at T=0 due to interactions.

cond-mat.mes-hall↗

arXiv1998

Interaction and Quantum Decoherence

We discuss a fundamental effect of the interaction-induced decoherence of the electron wave function in disordered metals. In the first part of the paper we consider a simple model of a quantum particle interacting with a bath of harmonic oscillators and analyze the physical origin of the effect. This exactly solvable model also allows to understand why the arguments against the existence of the effect at low temperatures fail. The second part of the paper is devoted to a rigorous analysis of quantum decoherence in disordered metals. We also discuss the relation of our results to the recent experiments on GaAs structures. The existence of a finite quantum decoherence rate at low $T$ implies that low dimensional disordered metals with generic parameters do not become insulators even at T=0.

cond-mat↗

arXiv1998

$π-$shifted magnetoconductance oscillations in mesoscopic superconducting-normal-heterostructures

Interference of proximity induced superconducting correlations in mesoscopic metallic rings is sensitive to the magnetic flux $Φ$ inside these rings. This is the reason for magnetoconductance oscillations in such systems. We detected experimentally and explained theoretically a novel effect: the phase of these oscillations can switch between 0 and $π$ depending on the resistance of intermetallic interfaces and temperature. The effect is due to a nontrivial interplay between the proximity induced enhancement of the local conductivity and the proximity induced suppression of the density of states at low energies.

cond-mat.supr-con↗

arXiv1998

Strong Tunneling and Coulomb Blockade in a Single-Electron Transistor

We have developed a detailed experimental study of a single-electron transistor in a strong tunneling regime. Although weakened by strong charge fluctuations, Coulomb effects were found to persist in all samples including one with the effective conductance 8 times higher than the quantum value (6.45 k$Ω$)$^{-1}$. A good agreement between our experimental data and theoretical results for the strong tunneling limit is found. A reliable operation of transistors with conductances 3-4 times larger than the quantum value is demonstrated.

cond-mat↗

arXiv1997

Strong Electron Tunneling through Mesoscopic Metallic Grains

We describe electron transport through small metallic grains with Coulomb blockade effects beyond the perturbative regime. For this purpose we study the real-time evolution of the reduced density matrix of the system. In the first part of the paper we present a diagrammatic expansion for not too high junction conductance, $h/4π^2e^2 R_t \lesssim 1$, in a basis of charge states. Quantum fluctuations renormalize system parameters and lead to finite lifetime broadening in the gate-voltage dependent differential conductance. We derive analytic results for the spectral density and the conductance in the limit where only two charge states play a role. In the second part of the paper we consider junctions with large conductance, $h/4e^2 R_t \gtrsim 1$. In this case contributions from all charge states, which broaden and overlap, become important. We analyze the problem in a quasiclassical approximation. The two complementary approaches cover the essential features of electron tunneling for all parameters.

cond-mat.mes-hall↗