arXiv subjects

V. M. Vinokur

Publications and source records attributed to V. M. Vinokur.

At least 73 records · Page 4Linked to original sources

arXiv2012

Comment on: "Vortex-assisted photon count and their magnetic field dependence in single-photon superconducting detectors" by L.N. Bulaevskii, M.J. Graf and V.G. Kogan, Phys. Rev. B 85, 014505 (2012)

In this Comment we show that the statements made in PRB85, 014505 (2012) regarding our work (PRL 100, 227007 (2008))) are incorrect because they result from model artifacts. We address the issues neglected in PRB85, 014505 (2012) and discuss their importance for a more consistent theory of thermally-activated hoping of vortices in thin films and the interpretation of experimental data.

cond-mat.supr-con↗

arXiv2011

Localization-Delocalization Transition and Current Fractalization

We develop an analytical theory of the localization-delocalization transition for a disordered Bose system, focusing on a Cooper-pair insulator. We consider a chain of small superconducting granules coupled via Josephson links and show that the low-temperature tunnelling transport of Cooper pairs is mediated by a self-generated environment of dipole excitations comprised of the same particles as the tunnelling charge carriers in accord with the early notion by Fleishman, Licciardello, and Anderson. We derive an analytical expression for the current-voltage characteristic and find that at temperatures, T, below the the charging energy of a single junction, E_c, the dc transport is completely locked by Coulomb blockade effect at all voltages except for a discrete set of resonant ones. At T>E_c the combined action of disorder and temperature unlocks the charge transport, since the environment excitation spectrum becomes quasi-continuous according to a Landau-Hopf-like scenario of turbulence, and the conductivity acquires an Arrhenius-like thermal activation form. The transition from the localized to delocalized behaviour occurs at T=E_c which corresponds to the onset of turbulence in the spectral flow of environmental excitations with Reynolds number Re=(k_B T/E_c)=1. The proposed theory breaks ground for a quantitative description of dynamic and quantum phase transitions in a wealth of physical systems ranging from cold atoms in optical lattices, through disordered films and wires to granular and nanopatterned materials.

cond-mat.mes-hall↗

arXiv2011

Superconducting phase transitions in ultrathin TiN films

We investigate transition to the superconducting state in the ultrathin titanium nitride films on approach to superconductor-insulator transition. Building on the complete account of quantum contributions to conductivity, we demonstrate that the resistance of thin superconducting films exhibits a non-monotonic temperature behaviour due to the competition between weak localization, electron-electron interaction, and superconducting fluctuations. We show that superconducting fluctuations give rise to an appreciable decrease in the resistance even at temperatures well exceeding the superconducting transition temperature, T_c, with this decrease being dominated by the Maki-Thompson process.The transition to a global phase-coherent superconducting state occurs via the Berezinskii-Kosterlitz-Thouless (BKT) transition, which we observe both by power-law behaviour in current-voltage characteristics and by flux flow transport in the magnetic field. The ratio T_{BKT}/T_c follows the universal Beasley-Mooij-Orlando relation. Our results call for revisiting the past data on superconducting transition in thin disordered films.

cond-mat.supr-con↗

arXiv2011

Far-from-equilibrium superconductor in fluctuational regime

We derive Ginzburg-Landau-like action for two-dimensional disordered superconductor under far-from-equilibrium conditions in a fluctuational regime. Then, utilizing it, we calculate fluctuation induced density of states, Maki-Thomson and Aslamazov-Larkin type contributions to the in-plane electrical conductivity. We apply our approach to thin superconducting film sandwiched between a gate and a substrate that have different temperatures and different electrochemical potentials.

cond-mat.supr-con↗

arXiv2011

Localized Andreev edge states in HgTe quantum wells

We investigate the interplay of superconductivity and the topological order in the topological insulator (TI) formed in HgTe-CdTe quantum wells coupled to the s-wave isotropic superconductor (SC) placed on top of CdTe layer. Proximity effect induces superconducting correlations in TI effecting classification of the TI electronic states. Depending on the strength of the coupling and the initial chemical potentials in SC and TI, the edge states either (i) become gapped, or (ii) hybridize into localized Andreev states, or else (iii) merge with the bulk states turning the TI into an anisotropic narrow-gap semiconductor.

cond-mat.supr-con↗

arXiv2011

Out-of-equilibrium heating of electron liquid: fermionic and bosonic temperatures

We investigate out-of-the equilibrium properties of the electron liquid in a two-dimensional disordered superconductor subject to the electric bias and temperature gradient. We calculate kinetic coefficients and Nyquist noise, and find that they are characterized by distinct effective temperatures: $T_{\mathrm{e}}$, characterizing single-particle excitations, $T_{\mathrm{Cp}}$, describing the Cooper pairs, and $T_{\mathrm{eh}}$, corresponding to electron-hole or dipole excitations. Tuning the ratio between the electric $j$ and thermal $j_{\mathrm{th}}$ currents and the boundary conditions one can heat different kind of excitations and control their corresponding temperatures. We propose the experimental setting for determining these effective temperatures.

cond-mat.str-el↗

arXiv2010

Pseudogap in a thin film of a conventional superconductor

A superconducting state is characterized by the gap in the electronic density of states which vanishes at the superconducting transition temperature Tc. It was discovered that in high temperature superconductors a noticeable depression in the density of states still remains even at temperatures above Tc; this feature being called pseudogap. Here we show that a pseudogap exists in a conventional superconductor: ultrathin titanium nitride films over a wide range of temperatures above Tc. Our study reveals that this pseudogap state is induced by superconducting fluctuations and favored by two-dimensionality and by the proximity to the transition to the insulating state. A general character of the observed phenomenon provides a powerful tool to discriminate between fluctuations as the origin of the pseudogap state, and other contributions in the layered high temperature superconductor compounds.

cond-mat.supr-con↗

arXiv2010

Fluctuoscopy of Disordered Two-Dimensional Superconductors

We revise the long studied problem of fluctuation conductivity (FC) in disordered two-dimensional superconductors placed in a perpendicular magnetic field by finally deriving the complete solution in the temperature-magnetic field phase diagram. The obtained expressions allow both to perform straightforward (numerical) calculation of the FC surface $δσ_{xx}^{(\mathrm{tot})}(T,H)$ and to get asymptotic expressions in all its qualitatively different domains. This surface becomes in particular non-trivial at low temperatures, where it is trough-shaped with $% δσ_{xx}^{(\mathrm{tot})}(T,H)<0$. In this region, close to the quantum phase transition, $δσ_{xx}^{(\mathrm{tot})}(T,H=\mathrm{const})$ is non-monotonic, in agreement with experimental findings. We reanalyzed and present comparisons to several experimental measurements. Based on our results we derive a qualitative picture of superconducting fluctuations close to $H_{\mathrm{c2}}(0) $ and T=0 where fluctuation Cooper pairs rotate with cyclotron frequency $ω_{c}\simΔ_{\mathrm{BCS}}^{-1}$ and Larmor radius $\sim ξ_{\mathrm{BCS}}$, forming some kind of quantum liquid with long coherence length $ξ_{\mathrm{QF}}\ggξ_{\mathrm{BCS}}$ and slow relaxation ($τ_{\mathrm{QF}}\gg\hbarΔ_{\mathrm{BCS}}^{-1}$).

cond-mat.supr-con↗

arXiv2010

Intrinsic non-linear conduction in the super-insulating state of thin TiN films

We investigate experimentally the electric transport at the insulating side of the superconductor to insulator transition in thin TiN-films. At temperatures T > 50 mK we observe an Arrhenius-type conductance, with an activation energy depending logarithmically on the sample size. At high bias the current voltage (I-V) characteristics display a large current jump into an electron heating dominated regime. For the largest samples, and below 50 mK we observe a low-bias power law I ~ V^alpha characteristics with an exponent alpha > 1 rapidly growing with decreasing temperature, which is expected for a binding-unbinding crossover of the charge-Berezinskii-Kosterlitz-Thouless type.

cond-mat.supr-con↗

arXiv2010

Nanopattern-stimulated superconductor-insulator transition in thin TiN films

We present the results of the comparative study of the influence of disorder on transport properties in continuous and nanoperforated TiN films. We show that nanopatterning turns a thin TiN film into an array of superconducting weak links and stimulates both, the disorder- and magnetic field-driven superconductor-to-insulator transitions, pushing them to lower degree of disorder. We find that nanopatterning enhances the role of the two-dimensional Coulomb interaction in the system transforming the originally insulating film into a more pronounced insulator. We observe magnetoresistance oscillations reflecting collective behaviour of the multiconnected nanopatterned superconducting film in the wide range of temperatures and uncover the physical mechanism of these oscillations as phase slips in superconducting weak link network.

cond-mat.supr-con↗

arXiv2010

Slow Crack Propagation in Heterogeneous Materials

Statistics and thermally activated dynamics of crack nucleation and propagation in a two-dimensional heterogeneous material containing quenched randomly distributed defects are studied theoretically. Using the generalized Griffith criterion we derive the equation of motion for the crack tip position accounting for dissipation, thermal noise and the random forces arising from the defects. We find that aggregations of defects generating long-range interaction forces (e.g., clouds of dislocations) lead to anomalously slow creep of the crack tip or even to its complete arrest. We demonstrate that heterogeneous materials with frozen defects contain a large number of arrested microcracks and that their fracture toughness is enhanced to the experimentally accessible time scales.

cond-mat.dis-nn↗

arXiv2010

Quantum Fluctuations and Dynamic Clustering of Fluctuating Cooper Pairs

We derive exact expressions for the fluctuation conductivity in two dimensional superconductors as a function of temperature and magnetic field in the whole fluctuation region above the upper critical field H_{c2}(T). Focusing on the vicinity of the quantum phase transition near zero temperature, we propose that as the magnetic field approaches the line near H_{c2}(0) from above, a peculiar dynamic state consisting of clusters of coherently rotating fluctuation Cooper-pairs forms and estimate the characteristic size and lifetime of such clusters. We find the zero temperature magnetic field dependence of the the transverse magnetoconductivity above H_{c2}(0) in layered superconductors.

cond-mat.supr-con↗

arXiv2010

Synchronized Andreev Transmission in Chains of SNS Junctions

We construct a nonequilibrium theory for the charge transfer through a diffusive array of alternating normal (N) and superconducting (S) islands comprising an SNSNS junction, with the size of the central S-island being smaller than the energy relaxation length. We demonstrate that in the nonequilibrium regime the central island acts as Andreev retransmitter with the Andreev conversions at both NS interfaces of the central island correlated via over-the-gap transmission and Andreev reflection. This results in a synchronized transmission at certain resonant voltages which can be experimentally observed as a sequence of spikes in the differential conductivity.

cond-mat.mes-hall↗

arXiv2010

Heating Effects in a Chain of Quantum Dots

We study heating effects in a chain of weakly coupled grains due to electron-hole pair creation. The main mechanism for the latter at low temperatures is due to inelastic electron cotunneling processes in the array. We develop a quantitative kinetic theory for these systems and calculate the array temperature profile as a function of grain parameters, bias voltage or current, and time and show that for nanoscale size grains the heating effects are pronounced and easily measurable in experiments. In the low- and high-voltage limits we solve the stationary heat-flux equation analytically. We demonstrate the over-heating hysteresis in the large-current or voltage regimes. In addition we consider the influence of a substrate on the system which acts as a heat sink. We show that nano dot chains can be used as highly sensitive thermometers over a broad range of temperatures.

cond-mat.mes-hall↗

arXiv2010

Coulomb-enhanced resonance transmission of quantum SINIS junctions

Coherent charge transfer through a ballistic gated SINIS junction is mediated by the resonant tunneling via the Andreev states. Extra charge accommodated on the Andreev levels partially compensates the charge induced by the gate voltage preserving the electron wavelength and maintaining the resonance conditions in a broad range of gate voltages. As a result, the transparency of the junction as well as the supercurrent trough it can be substantially increased as compared to the zero-Coulomb case.

cond-mat.supr-con↗

arXiv2010

Low temperature transport in tunnel junction arrays: Cascade energy relaxation

A theory of far-from-equilibrium transport in arrays of tunnel junctions is developed. We show that at low temperatures the energy relaxation ensuring tunneling current can become a cascade two-stage process. First, charge carriers lose their energy to a bosonic environment via non-phonon energy exchange. The role of such an environment can be taken by electromagnetic fluctuations or dipole excitations (electron-hole pairs). The environment, in its turn, relaxes the energy to the thermostat by means of phonon irradiation. We derive the current-voltage characteristics for the arrays and demonstrate that opening the energy gap in the spectrum of the environmental excitations completely suppresses the tunneling current. The consequences of the cascade relaxation in various physical systems are discussed.

cond-mat.str-el↗

arXiv2010

Synchronized Andreev Transmission in SNS Junction Arrays

cond-mat.mes-hall↗

arXiv2009

Hierarchical energy relaxation in mesoscopic tunnel junctions: Effect of nonequilibrium environment on low-temperature transport

We develop a theory of far from the equilibrium transport in arrays of tunnel junctions. We find that if the rate of the electron-electron interactions exceeds the rate of the electron-phonon energy exchange, the energy relaxation ensuring the charge transfer may occur sequentially. In particular, cotunneling transport in arrays of junctions is dominated by the relaxation via the intermediate bosonic environment, the electron-hole excitations, rather than by the electron-phonon mechanism. The current-voltage characteristics are highly sensitive to the spectrum of the environmental modes and to the applied bias, which sets the lower bound for the effective temperature. We demonstrate that the energy gap in the electron-hole spectrum which opens below some critical temperature T* due to long-range Coulomb interactions gives rise to the suppression of the tunneling current.

cond-mat.mes-hall↗