arXiv subjects

Andrei D. Zaikin

Publications and source records attributed to Andrei D. Zaikin.

At least 73 records · Page 4Linked to original sources

arXiv2007

Non-local electron transport and cross-resistance peak in NSN heterostructures

We develop a microscopic theory describing the peak in the temperature dependence of the non-local resistance of three-terminal NSN devices. This peak emerges at sufficiently high temperatures as a result of a competition between quasiparticle/charge imbalance and subgap (Andreev) contributions to the conductance matrix. Both the height and the shape of this peak demonstrate the power law dependence on the superconductor thickness $L$ in contrast to the zero-temperature non-local resistance which decays (roughly) exponentially with increasing $L$. A similar behavior was observed in recent experiments.

cond-mat.supr-con↗

arXiv2007

Spin-resolved crossed Andreev reflection in ballistic heterostructures

We theoretically analyze non-local effects in electron transport across three-terminal ballistic normal-superconducting-normal (NSN) structures with spin-active interfaces. Subgap electrons entering S-electrode from one N-metal may form Cooper pairs with their counterparts penetrating from another N-metal. This phenomenon of crossed Andreev reflection is highly sensitive to electron spins and yields a rich variety of properties of non-local conductance which we describe non-perturbatively at arbitrary interface transmissions, voltages and temperatures. Our results can be applied to hybrid structures with normal, ferromagnetic and half-metallic electrodes and can be directly tested in future experiments.

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arXiv2007

Crossed Andreev reflection at spin-active interfaces

With the aid of the quasiclassical Eilenberger formalism we develop a theory of non-local electron transport across three-terminal ballistic normal-superconducting-normal (NSN) devices with spin-active NS interfaces. The phenomenon of crossed Andreev reflection (CAR) is known to play the key role in such transport. We demonstrate that CAR is highly sensitive to electron spins and yields a rich variety of properties of non-local conductance which we describe non-perturbatively at arbitrary voltages, temperature, spin-dependent interface transmissions and their polarizations. Our results can be applied to multi-terminal hybrid structures with normal, ferromagnetic and half-metallic electrodes and can be directly tested in future experiments.

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arXiv2007

Nonlocal Andreev reflection at high transmissions

We analyze non-local effects in electron transport across three-terminal normal-superconducting-normal (NSN) structures. Subgap electrons entering S-electrode from one N-metal may form Cooper pairs with their counterparts penetrating from another N-metal. This phenomenon of crossed Andreev reflection -- combined with normal scattering at SN interfaces -- yields two different contributions to non-local conductance which we evaluate non-perturbatively at arbitrary interface transmissions. Both these contributions reach their maximum values at fully transmitting interfaces and demonstrate interesting features which can be tested in future experiments.

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arXiv2006

Weak localization in arrays of metallic quantum dots

Combining scattering matrix formalism with non-linear $σ$-model technique we analyze weak localization effects in arrays of chaotic quantum dots connected via barriers with arbitrary distribution of channel transmissions. With the aid of our approach we evaluate magnetoconductance of two arbitrarily connected quantum dots as well as of $N\times M$ arrays of identical quantum dots.

cond-mat.mes-hall↗

arXiv2006

Minigap, Parity Effect and Persistent Currents in SNS Nanorings

We have evaluated a proximity-induced minigap in the density of states (DOS) of SNS junctions and SNS nanorings at an arbitrary concentration of non-magnetic impurities. We have demonstrated that an isotropic energy minigap in the electron spectrum opens up already at arbitrarily weak disorder, while angle resolved DOS at higher energies can remain strongly anisotropic. The minigap value $ε_g$ can be tuned by passing a supercurrent through an SNS junction or by applying a magnetic flux $Φ$ to an SNS ring. A non-monotonous dependence of $ε_g$ on $Φ$ has been found at weak disorder. We have also studied persistent currents in isolated SNS nanorings. For odd number of electrons in the ring we have found a non-trivial current-phase (current-flux) relation which -- at relatively high disorder -- may lead to a $π$-junction state and spontaneous currents in the ground state of the system.

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arXiv2005

Comment on ``Influence Functional for Decoherence of Interacting Electrons in Disordered Conductors'' (cond-mat/0510563v1) and on related papers (cond-mat/0510556v1 and cond-mat/0510557v1)

Recently von Delft (cond-mat/0510563v1)(JvD) has successfully re-derived our influence functional for interacting electrons and claimed that within our approach he was able to obtain the electron decoherence rate that vanishes at T=0. In this Comment we demonstrate that this JvD's claim is in error, as it is based on ambiguous and uncontrolled manipulations violating basic principles of quantum theory, such as energy-time uncertainty relation, causality, fluctuation-dissipation theorem, detailed balance and the like. We also briefly address insufficient approximations employed by Marquardt {\it et al.} (cond-mat/0510556v1) and by von Delft {\it et al.} (cond-mat/0510557v1) and demonstrate that the results of all three papers in the limit T=0 are inconsistent with simple rules of algebra.

cond-mat.mes-hall↗

arXiv2005

Some novel effects in superconducting nanojunctions

In this paper we address several new developments in the theory of dc Josephson effect in superconducting weak links. We analyze an interplay between quantum interference effects and Andreev reflection in SNS nanojunctions with insulating barriers and demonstrate that such effects may qualitatively modify the Josephson current in such structures. We also investigate an impact of the parity effect on persistent currents in superconducting nanorings interrupted by a quantum point contact (QPC). In the limit of zero temperature and for the odd number of electrons in the ring we predict complete suppression of the supercurrent across QPC with one conducting mode. In nanorings with SNS junctions a $π$-state can occur for the odd number of electrons. Changing this number from even to odd yields spontaneous supercurrent in the ground state of such rings without any externally applied magnetic flux.

cond-mat.mes-hall↗

arXiv2005

Electron transport and current fluctuations in short coherent conductors

Employing a real time effective action formalism we analyze electron transport and current fluctuations in comparatively short coherent conductors in the presence of electron-electron interactions. We demonstrate that, while Coulomb interaction tends to suppress electron transport, it may {\it strongly enhance} shot noise in scatterers with highly transparent conducting channels. This effect of excess noise is governed by the Coulomb gap observed in the current-voltage characteristics of such scatterers. We also analyze the frequency dispersion of higher current cumulants and emphasize a direct relation between electron-electron interaction effects and current fluctuations in disordered mesoscopic conductors.

cond-mat.mes-hall↗

arXiv2005

Parity effect and spontaneous currents in superconducting nanorings

New physical effects emerge from an interplay between the electron parity number and persistent currents in superconducting nanorings. An odd electron, being added to the ring, produces a countercurrent which may substantially modify the ground state properties of the system. In superconducting nanorings with an embedded normal metal layer a novel ``$π/N$-junction'' state can occur for the odd number of electrons. Changing this number from even to odd yields spontaneous supercurrent in the ground state of such rings without any externally applied magnetic flux. Further peculiar features of the parity effect are expected in structures with resonant electron transport across the weak link.

cond-mat.mes-hall↗

arXiv2005

Parity-Affected Persistent Currents in Superconducting Nanorings

We argue that at sufficiently low temperatures T superconducting parity effect may strongly influence equilibrium persistent currents (PC) in isolated superconducting nanorings containing a weak link with few conducting modes. For a single channel quantum point contact at T=0 we predict a novel effect of parity-induced blocking of PC. In nanorings with SNS junctions a $π$-state can occur for the odd number of electrons. Changing this number from even to odd yields spontaneous supercurrent in the ground state of such rings without any externally applied magnetic flux.

cond-mat.mes-hall↗

arXiv2003

Low temperature decoherence by electron-electron interactions: Role of quantum fluctuations

We derive a general expression for the conductivity of a disordered conductor with electron-electron interactions (treated within the standard model) and evaluate the weak localization correction delta sigma_{wl} employing no approximations beyond the accuracy of the definition of delta sigma_{wl}. Our analysis applies to all orders in the interaction and extends our previous calculation by explicitly taking into account quantum fluctuations around the classical paths for interacting electrons (pre-exponent). We specifically address the most interesting low temperature limit and demonstrate that such fluctuations can only be important in the perturbative regime of short times while they are practically irrelevant for the Cooperon dynamics at longer times. We fully confirm our conclusion about the existence of interaction-induced decoherence of electrons at zero temperature for the problem in question. We also demonstrate irrelevance of a perturbative calculation by Aleiner et al. (AAV) [J. Low Temp. Phys. 126, 1377 (2002) and cond-mat/0110545] and discard AAV's critique of our earlier analysis.

cond-mat.mes-hall↗

arXiv2003

Electron transport through interacting quantum dots

We present a detailed theoretical investigation of the effect of Coulomb interactions on electron transport through quantum dots and double barrier structures connected to a voltage source via an arbitrary linear impedance. Combining real time path integral techniques with the scattering matrix approach we derive the effective action and evaluate the current-voltage characteristics of quantum dots at sufficiently large conductances. Our analysis reveals a reach variety of different regimes which we specify in details for the case of chaotic quantum dots. At sufficiently low energies the interaction correction to the current depends logarithmically on temperature and voltage. We identify two different logarithmic regimes with the crossover between them occurring at energies of order of the inverse dwell time of electrons in the dot. We also analyze the frequency-dependent shot noise in chaotic quantum dots and elucidate its direct relation to interaction effects in mesoscopic electron transport.

cond-mat.mes-hall↗

arXiv2002

Low-temperature Dephasing and Renormalization in Model Systems

We investigate low-temperature dephasing in several model systems, where a quantum degree of freedom is coupled to a bath. Dephasing, defined as the decay of the coherence of inital non-equilibrium states, also influences the dynamics of equilibrium correlation and response functions, as well as static interference effects. In particular in the latter case dephasing should be distinguished from renormalization effects. For illustration, and because of its relevance for quantum state engineering in dissipative environments, we first reconsider dephasing in spin-boson models. Next we review Caldeira-Leggett models, with applications, e.g., to persistent currents in mesoscopic rings. Then, we analyze the more general problem of a particle which interacts with a quantum field V(t,r(t)), the fluctuations of which are characterized by a dielectric function epsilon(omega,k). Finally, we compare this model, both the formulation as well as the results, to the problem of interacting electrons in a diffusive conductor.

cond-mat.mes-hall↗

arXiv2002

Interaction-Induced Quantum Dephasing in Mesoscopic Rings

Combining nonperturbative techniques with Monte Carlo simulations we demonstrate that quantum coherence effects for a particle on a ring are suppressed beyond a finite length $L_ϕ$ even at zero temperature if the particle is coupled to a diffusive electron gas by means of long range Coulomb interaction. This length is consistent with $L_ϕ$ derived from weak-localization-type of analysis.

cond-mat.mes-hall↗

arXiv2001

Comment on "Absence of electron dephasing at zero temperature"

The recent claim by Kirkpatrick and Belitz (cond-mat/0111398) that Ward identities could be used to prove the absence of electron dephasing at T=0 contains serious flaws. These authors try to draw conclusions about dephasing from an analysis of the diffuson, which is not sensitive to this process. The Cooperon, which does contain this information, is analyzed only in time reversal symmetric situations, which by assumption excludes any relaxation and dephasing. Hence, their analysis remains inconclusive for the problem in question.

cond-mat.mes-hall↗

arXiv2001

Quantum interference and supercurrent in multiple-barrier proximity structures

We analyze an interplay between the proximity effect and quantum interference of electrons in hybrid structures superconductor-normal metal-superconductor which contain several insulating barriers. We demonstrate that the dc Josephson current in these structures may change qualitatively due to quantum interference of electrons scattered at different interfaces. In junctions with few conducting channels mesoscopic fluctuations of the supercurrent are significant and its amplitude can be strongly enhanced due to resonant effects. In the many channel limit averaging over the scattering phase effectively suppresses interference effects for systems with {\it two} insulating barriers. In that case a standard quasiclassical approach describing scattering at interfaces by means of Zaitsev boundary conditions allows to reproduce the correct results. However, in systems with {\it three} or more barriers the latter approach fails even in the many channel limit. In such systems interference effects remain important in this limit as well. For short junctions these effects result in additional suppression of the Josephson critical current indicating the tendency of the system towards localization. For relatively long junctions interference effects may -- on the contrary -- enhance the supercurrent with respect to the case of independent barriers.

cond-mat.mes-hall↗

arXiv2001

Superconductor-insulator quantum phase transition in a single Josephson junction

The superconductor-to-insulator quantum phase transition in resistively shunted Josephson junctions is investigated by means of path-integral Monte Carlo simulations. This numerical technique allows us to directly access the (previously unexplored) regime of the Josephson-to-charging energy ratios E_J/E_C of order one. Our results unambiguously support an earlier theoretical conjecture, based on renormalization-group calculations, that at T -> 0 the dissipative phase transition occurs at a universal value of the shunt resistance R_S = h/4e^2 for all values E_J/E_C. On the other hand, finite-temperature effects are shown to turn this phase transition into a crossover, which position depends significantly on E_J/E_C, as well as on the dissipation strength and on temperature. The latter effect needs to be taken into account in order to reconcile earlier theoretical predictions with recent experimental results.

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