arXiv subjects

A. D. Zaikin

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

At least 19 recordsLinked to original sources

arXiv2017

Andreev levels as a quantum dissipative environment

We argue that at subgap energies quantum behavior of superconducting weak links can be exactly accounted for by an effective Hamiltonian for a Josephson particle in a quantum dissipative environment formed by Andreev levels. This environment can constitute an important source for intrinsic inelastic relaxation and dephasing in highly transparent weak links. We investigate the problem of macroscopic quantum tunneling in such weak links demonstrating that -- depending on the barrier transmission -- the supercurrent decay can be described by three different regimes: ($i$) weak intrinsic dissipation, ($ii$) strong intrinsic dissipation and ($iii$) strong capacitance renormalization. Crossover between quantum and thermally-assisted supercurrent decay regimes can also be strongly affected by the Andreev level environment.

cond-mat.supr-con↗

arXiv2013

Nonlocal transport and heating in superconductors under dual-bias conditions

We report on an experimental and theoretical study of nonlocal transport in superconductor hybrid structures, where two normal-metal leads are attached to a central superconducting wire. As a function of voltage bias applied to both normal-metal electrodes, we find surprisingly large nonlocal conductance signals, almost of the same magnitude as the local conductance. We demonstrate that these signals are the result of strong heating of the superconducting wire, and that under symmetric bias conditions, heating mimics the effect of Cooper pair splitting.

cond-mat.supr-con↗

arXiv2013

Current-biased Andreev interferometer

We theoretically investigate the behavior of Andreev interferometers with three superconducting electrodes in the current-biased regime. Our analysis allows to predict a number of interesting features of such devices, such as both hysteretic and non-hysteretic behavior, negative magnetoresistance and two different sets of singularities of the differential resistance at subgap voltages. In the non-hysteretic regime we find a pronounced voltage modulation with the magnetic flux which can be used for improving sensitivity of Andreev interferometers.

cond-mat.supr-con↗

arXiv2012

Andreev interferometer with three superconducting electrodes

We develop a quasiclassical theory of Andreev interferometers with three superconducting electrodes. Provided tunneling interface resistance between one superconducting electrode and the normal metal strongly exceeds two others, significant current sensitivity to the external magnetic flux is observed only at subgap voltages. If all barrier conductances are comparable, multiple Andreev reflection comes into play and substantial current modulation can be achieved in both subgap and overgap voltage regimes. Our analysis reveals a large variety of interesting features which can be used for performance optimization of Andreev interferometers.

cond-mat.supr-con↗

arXiv2012

Non-local electron transport and Coulomb effects in three-terminal metallic conductors

We demonstrate a close relation between Coulomb effects in non-local electron transport and non-local shot noise in three-terminal metallic conductors. Provided the whole structure is normal, cross-correlations in shot noise are negative and Coulomb interaction tends to suppress both local and non-local conductances of the system. The behavior of normal-superconducting-normal structures at subgap energies is entirely different. In the tunneling limit non-local differential conductance of such systems are found to have an S-like shape and can turn negative at non-zero bias. At high transmissions crossed Andreev reflection yields positive noise cross-correlations and Coulomb anti-blockade of non-local electron transport.

cond-mat.mes-hall↗

arXiv2012

Coulomb blockade of non-local electron transport in metallic conductors

We consider a metallic wire coupled to two metallic electrodes via two junctions placed nearby. A bias voltage applied to one of such junctions alters the electron distribution function in the wire in the vicinity of another junction thus modifying both its noise and the Coulomb blockade correction to its conductance. We evaluate such interaction corrections to both local and non-local conductances demonstrating non-trivial Coulomb anomalies in the system under consideration. Experiments on non-local electron transport with Coulomb effects can be conveniently used to test inelastic electron relaxation in metallic conductors at low temperatures.

cond-mat.str-el↗

arXiv2011

Current fluctuations in composite conductors: Beyond the second cumulant

Employing the non-linear $σ$-model we analyze current fluctuations in coherent composite conductors which contain a diffusive element in-between two tunnel barriers. For such systems we explicitly evaluate the frequency-dependent third current cumulant which also determines the leading Coulomb interaction correction to shot noise. Our predictions can be directly tested in future experiments.

cond-mat.mes-hall↗

arXiv2010

Current noise and Coulomb effects in superconducting contacts

We derive an effective action for contacts between superconducting terminals with arbitrary transmission distribution of conducting channels. In the case of normal-superconducting (NS) contacts we evaluate interaction correction to Andreev conductance and demonstrate a close relation between Coulomb effects and shot noise in these systems. In the case of superconducting (SS) contacts we derive the electron-electron interaction correction to the Josephson current. At $T=0$ both corrections are found to vanish for fully transparent NS and SS contacts indicating the absence of Coulomb effects in this limit.

cond-mat.supr-con↗

arXiv2010

Fluctuations of the Josephson current and electron-electron interactions in superconducting weak links

We derive a microscopic effective action for superconducting contacts with arbitrary transmission distribution of conducting channels. Provided fluctuations of the Josephson phase remain sufficiently small our formalism allows to fully describe fluctuation and interaction effects in such systems. As compared to the well studied tunneling limit our analysis yields a number of qualitatively new features which occur due to the presence of subgap Andreev bound states in the system. We investigate the equilibrium supercurrent noise and evaluate the electron-electron interaction correction to the Josephson current across superconducting contacts. At T=0 this correction is found to vanish for fully transparent contacts indicating the absence of Coulomb effects in this limit.

cond-mat.supr-con↗

arXiv2009

Superconductivity in one dimension

Superconducting properties of metallic nanowires can be entirely different from those of bulk superconductors because of the dominating role played by thermal and quantum fluctuations of the order parameter. For superconducting wires with diameters below $ \sim 50$ nm quantum phase slippage is an important process which can yield a non-vanishing wire resistance down to very low temperatures. Further decrease of the wire diameter, for typical material parameters down to $\sim 10$ nm, results in proliferation of quantum phase slips causing a sharp crossover from superconducting to normal behavior even at T=0. A number of interesting phenomena associated both with quantum phase slips and with the parity effect occur in superconducting nanorings. We review recent theoretical and experimental activities in the field and demonstrate dramatic progress in understanding of the phenomenon of superconductivity in quasi-one-dimensional nanostructures.

cond-mat.supr-con↗

arXiv2009

Magnetic field and contact resistance dependence of non-local charge imbalance

Crossed Andreev reflection (CAR) in metallic nanostructures, a possible basis for solid-state electron entangler devices, is usually investigated by detecting non-local voltages in multi-terminal superconductor/normal metal devices. This task is difficult because other subgap processes may mask the effects of CAR. One of these processes is the generation of charge imbalance (CI) and the diffusion of non-equilibrium quasi-particles in the superconductor. Here we demonstrate a characteristic dependence of non-local CI on a magnetic field applied parallel to the superconducting wire, which can be understood by a generalization of the standard description of CI to non-local experiments. These results can be used to distinguish CAR and CI and to extract CI relaxation times in superconducting nanostructures. In addition, we investigate the dependence of non-local CI on the resistance of the injector and detector contacts and demonstrate a quantitative agreement with a recent theory using only material and junction characteristics extracted from separate direct measurements.

cond-mat.mes-hall↗

arXiv2009

Shot noise and Coulomb blockade of Andreev reflection

We derive low energy effective action for a short coherent conductor between normal (N) and superconducting (S) reservoirs. We evaluate interaction correction $δG$ to Andreev conductance and demonstrate a close relation between Coulomb effects and shot noise in NS systems. In the diffusive limit doubling of both shot noise power and charge of the carriers yields $|δG|$ four times bigger than in the normal case. Our predictions can be directly tested in future experiments.

cond-mat.supr-con↗

arXiv2009

Non-local Andreev reflection under ac bias

We theoretically analyze non-local electron transport in multi-terminal normal-metal-superconductor-normal-metal (NSN) devices in the presence of an external ac voltage bias. Our analysis reveals a number of interesting effects, such as, e.g., photon-assisted violation of balance between crossed Andreev reflection (CAR) and elastic cotunneling (EC). We demonstrate that at sufficiently small (typically subgap) frequencies of an external ac signal and at low temperatures the non-local conductance of the NSN device turns negative implying that in this regime CAR contribution to the non-local current dominates over that of EC. Our predictions can be directly tested in future experiments.

cond-mat.supr-con↗

arXiv2009

Crossed Andreev reflection and charge imbalance in diffusive NSN structures

We formulate a microscopic theory of non-local electron transport in three-terminal diffusive normal-superconducting-normal (NSN) structures with arbitrary interface transmissions. At low energies $\varepsilon$ we predict strong enhancement of non-local spectral conductance $g_{12} \propto 1/\varepsilon$ due to quantum interference of electrons in disordered N-terminals. In contrast, non-local resistance $R_{12}$ remains smooth at small $\varepsilon$ and, furthermore, is found to depend neither on parameters of NS interfaces nor on those of N-terminals. At higher temperatures $R_{12}$ exhibits a peak caused by the trade-off between charge imbalance and Andreev reflection. Our results are in a good agreement with recent experimental observations and can be used for quantitative analysis of future experiments.

cond-mat.supr-con↗

arXiv2008

Weak localization in a system with a barrier: Dephasing and weak Coulomb blockade

We non-perturbatively analyze the effect of electron-electron interactions on weak localization (WL) in relatively short metallic conductors with a tunnel barrier. We demonstrate that the main effect of interactions is electron dephasing which persists down to T=0 and yields suppression of WL correction to conductance below its non-interacting value. Our results may account for recent observations of low temperature saturation of the electron decoherence time in quantum dots.

cond-mat.mes-hall↗

arXiv2007

Non-local Andreev reflection in superconducting quantum dots

With the aid of the Keldysh technique we develop a microscopic theory of non-local electron transport in three-terminal NSN structures consisting of a chaotic superconducting quantum dot attached to one superconducting and two normal electrodes. Our theory fully accounts for non-equilibrium effects and disorder in a superconducting terminal. We go beyond perturbation theory in tunneling and derive a general expression for the system conductance matrix which remains valid in both weak and strong tunneling limits. We demonstrate that the proximity effect yields a decrease of crossed Andreev reflection (CAR). Beyond weak tunneling limit the contribution of CAR to the non-local conductance does not cancel that of direct electron transfer between two normal terminals. We argue that temperature dependence of the non-local resistance of NSN devices is determined by the two competing processes -- Andreev reflection and charge imbalance -- and it has a pronounced peak occurring at the crossover between these two processes. This behavior is in a good agreement with recent experimental observations.

cond-mat.supr-con↗

arXiv2005

Coulomb Effects on Electron Transport and Shot Noise in Hybrid Normal-Superconducting Metallic Structures

We analyze the effect of electron-electron interactions on Andreev current and shot noise in diffusive hybrid structures composed of a normal metal attached to a superconductor via a weakly transmitting interface. We demonstrate that at voltages/temperatures below the Thouless energy of a normal metal Coulomb interaction yields a reduction of both Andreev current and its noise by a constant factor which essentially depends on the system dimensionality. For quasi-1d structures this factor is $\sim N_{\rm Ch}^{8/g}$, where $N_{\rm Ch}$ and $g$ are respectively the number of conducting channels and dimensionless conductance of a normal metal. At voltages above the Thouless energy the interaction correction to Andreev current and shot noise acquires an additional voltage dependence which turns out to be a power-law in the quasi-1d limit.

cond-mat.mes-hall↗

arXiv2004

Statistics of Current Fluctuations and Electron-Electron Interactions in Mesoscopic Coherent Conductors

We formulate a general path integral 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 the 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 ${\cal S}_3$. We also analyze the behavior of the second cumulant of the current operator ${\cal S}_2$ (current noise) in the presence of electron-electron interactions. In a wide range of parameters we obtain explicit universal dependencies of ${\cal S}_2$ 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↗