arXiv subjects

A. V. Andreev

Publications and source records attributed to A. V. Andreev.

At least 91 records · Page 5Linked to original sources

arXiv2006

Suppression of superconductivity due to non-perturbative saddle points in the nonlinear $σ$-model

We study superconductivity suppression due to thermal fluctuations in disordered wires using the replica nonlinear $σ$-model ($NLσM$). We show that in addition to the thermal phase slips there is another type of fluctuations that result in a finite resistivity. These fluctuations are described by saddle points in $NLσM$ and cannot be treated within the Ginzburg-Landau approach. The contribution of such fluctuations to the wire resistivity is evaluated with exponential accuracy. The magnetoresistance associated with this contribution is negative.

cond-mat.supr-con↗

arXiv2006

Statistics of speckle patterns

We develop a general method for calculating statistical properties of the speckle pattern of coherent waves propagating in disordered media. In some aspects this method is similar to the Boltzmann-Langevin approach for the calculation of classical fluctuations. We apply the method to the case where the incident wave experiences many small angle scattering events during propagation, but the total angle change remains small. In many aspects our results for this case are different from results previously known in the literature. The correlation function of the wave intensity at two points separated by a distance $r$, has a long range character. It decays as a power of $r$ and changes sign. We also consider sensitivities of the speckles to changes of external parameters, such as the wave frequency and the incidence angle.

cond-mat.mes-hall↗

arXiv2005

Quantum phase transitions across p-wave Feshbach resonance

We study a single-species polarized Fermi gas tuned across a narrow p-wave Feshbach resonance. We show that in the course of a BEC-BCS crossover the system can undergo a magnetic field-tuned quantum phase transition from a p_x-wave to a p_x+i p_y-wave superfluid. The latter state, that spontaneously breaks time-reversal symmetry, furthermore undergoes a topological p_x+ i p_y to p_x+ i p_y transition at zero chemical potential μ. In two-dimensions, for μ>0 it is characterized by a Pfaffian ground state exhibiting topological order and non-Abelian excitations familiar from fractional quantum Hall systems.

cond-mat.supr-con↗

arXiv2005

Quantum Charge Fluctuations in a Superconducting Grain

We consider charge quantization in a small superconducting grain that is contacted by a normal-metal electrode and is controlled by a capacitively coupled gate. At zero temperature and zero conductance $G$ between the grain and the electrode, the charge $Q$ as a function of the gate voltage $V_g$ changes in steps. The step height is $e$ if $Δ<E_c$, where $Δ$ and $E_c$ are, respectively, the superconducting gap and the charging energy of the grain. Quantum charge fluctuations at finite conductance remove the discontinuity in the dependence of $Q$ on $V_g$ and lead to a finite step width $\propto G^2Δ$. The resulting shape of the Coulomb blockade staircase is of a novel type. The grain charge is a continuous function of $V_g$ while the differential capacitance, $dQ/dV_g$, has discontinuities at certain values of the gate voltage. We determine analytically the shape of the Coulomb blockade staircase also at non-zero temperatures.

cond-mat.mes-hall↗

arXiv2004

Nonequilibrium dynamics and thermodynamics of a degenerate Fermi gas across a Feshbach resonance

We consider a two-species degenerate Fermi gas coupled by a diatomic Feshbach resonance. We show that the resulting superfluid can exhibit a form of coherent BEC-to-BCS oscillations in response to a nonadiabatic change in the system's parameters, such as for example a sudden shift in the position of the Feshbach resonance. In the narrow resonance limit, the resulting soliton-like collisionless dynamics can be calculated analytically. In equilibrium the thermodynamics can be accurately computed across the full range of BCS-BEC crossover, with corrections controlled by the ratio of the resonance width to the Fermi energy.

cond-mat.supr-con↗

arXiv2004

Estimation of the amount of the nuclear transformation products formed under explosion-induced compression of a substance to the superdense state

In the present work carried out at the Electrodynamics Laboratory Proton-21 with the use of X-ray electron probe microanalysis (XEPMA) and glow-discharge mass spectrometry (GDMS) techniques, we study the chemical composition of a substance formed as a result of the explosion-induced compression of solid targets and deposited on the surfaces of accumulating screens. We established that the explosion products contain chemical elements which were not included in the composition of the initial materials of targets and accumulating screens or were included in them as impurities in quantities by 3...7 and more orders in magnitude less than those detected after the experiment. We conclude that the regular appearance of chemical elements, which were not included in the composition of the initial materials of targets and accumulating screens, in the explosion products is the consequence of a nuclear transformation of a part of their material, i.e., is the fact testifying to both the running of the nucleosynthesis reactions upon the explosion-induced destruction of targets and to the first realized possibility of controlled creation of the conditions for their running in a laboratory setup.

nucl-ex↗

arXiv2004

Coulomb-blockade-induced bound quasiparticle states in a double-island qubit

We study the low temperature thermodynamic properties of a superconducting double-island qubit. For an odd number of electrons in the device, the ground state corresponds to the intrinsic quasiparticle bound to the tunneling contact. The ground state is separated from the continuum of excited states by a finite gap of order of the Josephson energy E_J. The presence of the bound quasiparticle state results in a nonmonotonic temperature dependence of the width of the transition region between Coulomb blockade plateaus. The minimum width occurs at the ionization temperature of the bound state, T_i\sim E_J/\ln(\sqrt{ΔE_J}/δ), with Δand δbeing respectively the superconducting gap and single particle mean level spacing in the island. For an even number of electrons in the system, we show that the Coulomb enhancement of the Josephson energy can be significantly stronger than that in the case of a single grain coupled to a superconducting lead. If the electrostatic energy favors a single broken Cooper pair, the resulting quasiparticles are bound to the contact with an energy that is exponentially small in the inverse dimensionless conductance.

cond-mat.mes-hall↗

arXiv2003

Coulomb drag by small momentum transfer between quantum wires

We demonstrate that in a wide range of temperatures Coulomb drag between two weakly coupled quantum wires is dominated by processes with a small interwire momentum transfer. Such processes, not accounted for in the conventional Luttinger liquid theory, cause drag only because the electron dispersion relation is not linear. The corresponding contribution to the drag resistance scales with temperature as T^2 if the wires are identical, and as T^5 if the wires are different.

cond-mat.mes-hall↗

arXiv2003

Mesoscopic charging effects in the $σ$-model for granular metals

We derive the $σ$-model for granular metals. It is valid for any relation between the temperature, $T$, and the grain mean level spacing. The continuum limit of the $σ$-model describes non-perturbative charging effects in homogeneous disordered metals. The $σ$-model action contains a novel term which is crucial for studying Coulomb blockade effects. Topological properties of the $σ$-model encoding charge discreteness are studied. For $T$ below the escape rate from the grain, $Γ$, Coulomb blockade effects are described by solitons of the $Q$-matrix which are delocalized in real space. At $T> Γ$ the solitons transform into phase instantons localized at a single tunneling contact.

cond-mat.mes-hall↗

arXiv2003

Dynamical symmetry breaking as the origin of the zero-$dc$-resistance state in an $ac$-driven system

Under a strong $ac$ drive the zero-frequency linear response dissipative resistivity $ρ_{d}(j=0)$ of a homogeneous state is allowed to become negative. We show that such a state is absolutely unstable. The only time-independent state of a system with a $ρ_{d}(j=0)<0$ is characterized by a current which almost everywhere has a magnitude $j_{0}$ fixed by the condition that the nonlinear dissipative resistivity $ρ_{d}(j_{0}^{2})=0$. As a result, the dissipative component of the $dc$ electric field vanishes. The total current may be varied by rearranging the current pattern appropriately with the dissipative component of the $dc$-electric field remaining zero. This result, together with the calculation of Durst \emph{et. al.}, indicating the existence of regimes of applied $ac$ microwave field and $dc$ magnetic field where $ρ_{d}(j=0)<0$, explains the zero-resistance state observed by Mani \emph{et. al.} and Zudov \emph{et. al.}.

cond-mat.mes-hall↗

arXiv2002

Two-loop approximation in the Coulomb blockade problem

We study Coulomb blockade (CB) oscillations in the thermodynamics of a metallic grain which is connected to a lead by a tunneling contact with a large conductance $g_0$ in a wide temperature range, $E_Cg_0^4 e^{-g_0/2}<T<E_C$, where $E_C$ is the charging energy. Using the instanton analysis and the renormalization group we obtain the temperature dependence of the amplitude of CB oscillations which differs from the previously obtained results. Assuming that at $T < E_Cg_0^4 e^{-g_0/2}$ the oscillation amplitude weakly depends on temperature we estimate the magnitude of CB oscillations in the ground state energy as $E_Cg_0^4 e^{-g_0/2}$.

cond-mat.mes-hall↗

arXiv2002

Full counting statistics of a charge pump in the Coulomb blockade regime

We study the full charge counting statistics of a charge pump based on a nearly open single electron transistor. The problem is mapped onto an exactly soluble problem of a g=1/2 non-equilibrium Luttinger liquid with an impurity. We obtain an analytic expression for the generating function of the transmitted charge for an arbitrary pumping strength. Even though this model contains fractionally charged excitations only integer transmitted charges can be observed during finite observation times.

cond-mat.mes-hall↗

arXiv2002

Coulomb blockade in metallic grains at large conductance: beyond the zero-dimensional limit

We consider mesoscopic fluctuations of the Coulomb blockade oscillations in a disordered metallic grain in an external magnetic field coupled to a metallic lead by a tunneling contact with a large conductance $g_T$ and capacitively coupled to a gate. For a finite mean level spacing $δ$ in the grain and at temperatures $T \gg δ$ we obtain the oscillatory part of the correlator of thermodynamic potentials at different values of the gate voltage. The correlations decay algebraically with the gate voltage difference in contrast to the exponential decay that would result from the mean-field treatment of the Coulomb interaction. The results are valid beyond the zero-dimensional limit and describe the crossover between the unitary and orthogonal ensembles.

cond-mat.mes-hall↗

arXiv2002

Coulomb blockade in metallic grains at large conductance

We study Coulomb blockade effects in the thermodynamic quantities of a weakly disordered metallic grain coupled to a metallic lead by a tunneling contact with a large conductance $g_T$. We consider the case of broken time-reversal symmetry and obtain expressions for both the {\em ensemble averaged} amplitude of the Coulomb blockade oscillations of the thermodynamic potential and the correlator of its {\em mesoscopic fluctuations} for a finite mean level spacing $δ$ in the grain. We develop a novel method which allows for an exact evaluation of the functional integral arising from disorder averaging. The results and the method are applicable in the temperature range $δ\ll T \ll E_C$.

cond-mat.mes-hall↗

arXiv2002

Thermopower of a single electron transistor in the regime of strong inelastic cotunneling

We study Coulomb blockade oscillations of thermoelectric coefficients of a single electron transistor based on a quantum dot strongly coupled to one of the leads by a quantum point contact. At temperatures below the charging energy E_C the transport of electrons is dominated by strong inelastic cotunneling. In this regime we find analytic expressions for the thermopower as a function of temperature T and the reflection amplitude $r$ in the contact. In the case when the electron spins are polarized by a strong external magnetic field, the thermopower shows sinusoidal oscillations as a function of the gate voltage with the amplitude of the order of $e^{-1}|r|\frac{T}{E_C}$. We obtain qualitatively different results in the absence of the magnetic field. At temperatures between $E_C$ and $E_C|r|^2$ the thermopower oscillations are sinusoidal with the amplitude of order $e^{-1}|r|^2 \ln \frac{E_C}{T}$. On the other hand, at $T\ll E_C|r|^2$ we find non-sinusoidal oscillations of the thermopower with the amplitude $\sim e^{-1} |r| \sqrt{T/E_C} \ln(E_C/T)$.

cond-mat.mes-hall↗

arXiv2001

Zero-bias anomaly in disordered wires

We calculate the low-energy tunneling density of states $ν(ε, T)$ of an $N$-channel disordered wire, taking into account the electron-electron interaction non-perturbatively. The finite scattering rate $1/τ$ results in a crossover from the Luttinger liquid behavior at higher energies, $ν\proptoε^α$, to the exponential dependence $ν(ε, T=0)\propto \exp{(-ε^*/ε)}$ at low energies, where $ε^*\propto 1/(N τ)$. At finite temperature $T$, the tunneling density of states depends on the energy through the dimensionless variable $ε/\sqrt{ε^* T}$. At the Fermi level $ν(ε=0,T) \propto \exp (-\sqrt{ε^*/T})$.

cond-mat.mes-hall↗

arXiv2001

Zero-bias anomaly in two-dimensional electron layers and multiwall nanotubes

The zero-bias anomaly in the dependence of the tunneling density of states $ν(ε)$ on the energy $ε$ of the tunneling particle for two- and one-dimensional multilayered structures is studied. We show that for a ballistic two-dimensional (2D) system the first order interaction correction to DOS due to the plasmon excitations studied by Khveshchenko and Reizer is partly compensated by the contribution of electron-hole pairs which is twice as small and has the opposite sign. For multilayered systems the total correction to the density of states near the Fermi energy has the form $δν/ν_0 = {max} (| ε|, ε^*)/4ε_F$, where $ε^*$ is the plasmon energy gap of the multilayered 2D system. In the case of one-dimensional conductors we study multiwall nanotubes with the elastic mean free path exceeding the radius of the nanotube. The dependence of the tunneling density of states energy, temperature and on the number of shells is found.

cond-mat.mes-hall↗

arXiv2000

Coulomb Blockade Oscillations in the Thermopower of Open Quantum Dots

We consider Coulomb blockade oscillations of thermoelectric coefficients of a single electron transistor based on a quantum dot strongly coupled to one of the leads. Analytic expression for the thermopower as a function of temperature $T$ and the reflection amplitude $r$ in the quantum point contact is obtained. Two regimes can be identified: $T \ll E_C|r|^2$ and $T \gg E_C |r|^2$, where $E_C$ is the charging energy of the dot. The former regime is characterized by weak logarithmic dependence of the thermopower on the reflection coefficient, in the latter the thermopower is linear in the reflection coefficient $|r|^2$ but depends on temperature only logarithmically.

cond-mat.mes-hall↗