arXiv subjects

S. I. Shevchenko

Publications and source records attributed to S. I. Shevchenko.

At least 19 recordsLinked to original sources

arXiv2026

Non-stationary longitudinal Josephson effect in electron-hole bilayers

The non-stationary longitudinal Josephson effect in bilayer systems with pairing of spatially separated electrons and holes is investigated. The tunneling current between two (right and left) weakly coupled electron-hole condensates is analyzed in the presence of an external voltage applied along the layers. Two limiting regimes are considered: the high-density regime, where pairing occurs in momentum space similarly to conventional superconductors, and the low-density regime corresponding to a Bose-Einstein condensate of spatially indirect excitons. Using the tunneling Hamiltonian approach, expressions for the quasiparticle, superconducting and interference contributions to the tunneling current are derived. It is shown that in the high-density limit the quasiparticle and interference currents vanish at zero temperature below a threshold voltage determined by the energy gap, so that only the supercurrent remains. In contrast, in the low-density regime the gapless spectrum of collective excitations leads to finite dissipative contributions even at zero temperature, resulting in damping of Josephson oscillations. For spatially separated tunneling barriers with distance exceeding the coherence length, phase jumps occur at each barrier, resulting in voltage oscillations across the electron and hole barriers and a non-sinusoidal current-phase relation governed by the critical currents of the two barriers.

cond-mat.supr-con↗

arXiv2025

Longitudinal Josephson effect in systems with pairing of spatially separated electrons and holes

Longitudinal non-dissipative current states in bilayer electron-hole systems in the presence of potential barriers that divide the system into left and right sides was investigated. The consideration is performed both for the case of weak carrier coupling (high density) and strong coupling (low density). It is shown that in the high-density limit, the critical current is proportional to the product of the transparencies of the barriers in the electron and hole layers, whereas in the low-density limit, the current is inversely proportional to the sum of the heights of the potential barriers.

cond-mat.mes-hall↗

arXiv2023

On the electric charge of quantized vortices and the dipole moment of vortex pairs and rings in a magnetic field

It is shown that, in the presence of a magnetic field, a quantized vortex line in a superfluid liquid acquires a linear polarization charge, which is localized near the vortex axis over a length on the order of the coherence length. It is found that the total charge of a rectilinear vortex is nonzero, while the vortex pair and vortex ring have a nonzero dipole moment. The electric fields of rectilinear vortices near the end surface of a cylindrical vessel filled with a superfluid liquid are calculated. The electric polarization of superfluid systems in the presence of thermally activated vortex pairs and vortex rings has been studied. It is shown that such a polarization arises in the presence of relative motion of the normal and superfluid components.

cond-mat.other↗

arXiv2022

Supersolid induced by dislocations with superfluid cores (Review article)

Dislocation model of the supersolid state of $^4$He was proposed in 1987 by one of the authors of the review. The model obtained strong support by numerous experimental and theoretical investigations from 2007 to date. In these investigations the validity of the idea put forward in 1987 was confirmed, and new conceptions of superclimb of dislocations and of the giant isochoric compressibility or the syringe effect were proposed. In this paper we review main achievements of theoretical and experimental studies of dislocation-induced supersolid and present current understanding of this phenomenon.

cond-mat.quant-gas↗

arXiv2021

Stationary waves in a superfluid gas of electron-hole pairs in bilayers

Stationary waves in the condensate of electron-hole pairs in the $n-p$ bilayer system are studied. The system demonstrates the transition from a uniform (superfluid) to a nonuniform (supersolid) state. The precursor of this transition is the appearance of the roton-type minimum in the collective mode spectrum. Stationary waves occur in the flow of the condensate past an obstacle. It is shown that the roton-type minimum manifests itself in a rather complicated stationary wave pattern with several families of crests which cross one another. It is found that the stationary wave pattern is essentially modified under variation in the density of the condensate and under variation in the flow velocity. It is shown that the pattern is formed in the main part by shortwave modes in the case of a point obstacle. The contribution of longwave modes is clearly visible in the case of a weak extended obstacle, where the stationary wave pattern resembles the ship wave pattern.

cond-mat.mes-hall↗

arXiv2020

Transition to a supersolid phase in a two-dimensional dilute gas of electron-hole pairs

Using coherent-state formalism (the Keldysh formalism), the article describes a transition from a homogeneous superfluid state to a supersolid state in a two-dimensional dilute gas of electron-hole pairs with spatially separated components. Such a transition is heralded by the appearance of a roton-type minimum in the collective excitation spectrum, which touches the abscissa axis as the distance between the layers or the pair density increases. This signals the instability of the system with respect to the appearance of a spatial modulation of the pair density. It has been found that a first-order transition to a hexagonal supersolid phase takes place a little earlier. A theory without phenomenological constants has been developed for an arbitrary relation between the effective masses of an electron and a hole. A phase diagram for the system has been plotted in the variables "the chemical potential of pairs - the distance between the layers". It has been shown that there is a jump in the average density of the condensate during the phase transition. It has been established that with an increase in the chemical potential, the inhomogeneous phase breaks up into high-density regions surrounded by lines at which the density becomes zero, with these lines forming a continuous network.

cond-mat.mes-hall↗

arXiv2020

Vortex generation in a superfluid gas of dipolar chains in crossed electric and magnetic fields

Crossed electric and magnetic fields influence dipolar neutral particles in the same way as the magnetic field influences charged particles. The effect of crossed fields is proportional to the dipole moment of the particle (inherent or induced). We show that this effect is quite spectacular in a multilayer system of polar molecules. In this system molecules may bind in chains. At low temperature the gas of chains becomes the superfluid one. The crossed fields then induce vortices in the superfluid gas of chains. The density of vortices is proportional to the number of particles in the chain. The effect can be used for monitoring the formation and destruction of chains in multilayer dipolar gases.

cond-mat.quant-gas↗

arXiv2019

Berry phase caused by nondissipative drag of superflow in a Bose qubit

A microscopic theory of superfluid drag in a two-component Bose gas is developed. The drag factor is shown to be proportional to the square root of the gas parameter. Basing on the similarity between the drag force and vector potential of magnetic field we propose how the superfluid drag can be used to detect a Berry phase in a Bose counterpart of the Josephson charge qubit. We consider a system in which the drag component, situated inside the drive component, is confined in two half-ring traps separated by two Josephson barriers. Under cyclic adiabatic change of Josephson coupling parameters and an asymmetry of two traps a Berry phase is generated. This phase can be observed though measurements of relative number of atoms in two traps. The Berry phase depends on the drag factor and its detection can be used for determining the value of the drag.

cond-mat.soft↗

arXiv2019

Superheat conductivity and electric activity of superfluid systems

In this article it is shown that in He\nobreakdash-II placed in a magnetic field $\mathbf{H}$, the heat flow under the influence of a temperature gradient $\nabla T$ causes appearance of an electric field $\mathbf{E}\sim\mathbf{H}\times\nabla T$. This effect occurs in superfluid dielectric systems due to their specific property named superheat conductivity. The magnitude of the electric field significantly depends on the shape of the helium sample and the magnetic field direction relative to the sample. The effect exists both at static and non-stationary temperature gradient (e. g. during propagation of second sound).

cond-mat.other↗

arXiv2018

Non-stationary thermal electromotive force generated by third sound

It is predicted that oscillations of temperature during propagation of third sound in a thin superfluid film cause appearance of an alternating electric field in the surrounding space (a peculiar non-stationary thermoelectric effect). The magnitude of this field depends significantly on the substrate type and the method of its coating. It is shown that the differential thermal EMF (the ratio of electric potential amplitude to the film temperature amplitude) can exceed such one in metals and reach $10^{-4}$ V/K.

cond-mat.other↗

arXiv2016

Superfluidity of a rarefied gas of electron-hole pairs in a bilayer system

The conditions of stability of the superfluid phase in double layer systems with pairing of spatially separated electrons and holes in the low density limit are studied. The general expression for the collective excitation spectrum is obtained. It is shown that under increase in the distance $d$ between the layers the minimum emerges in the excitation spectrum. When d reaches the critical value the superfluid state becomes unstable relative to the formation of a kind of the Wigner crystal state. The same instability occurs at fixed d under increase in the density of carries. It is established that the critical distance and the critical density are related to each other by the inverse power function. The impact of the impurities on the temperature of the superfluid transition is investigated. The impact is found weak at the impurity concentration smaller than the density of the pairs. It is shown that in the rarefied system the critical temperature T_c = 100 K can be reached.

cond-mat.mes-hall↗

arXiv2015

On the dipole moment of quantized vortices generated by flows

The polarization charge $ρ$ of an inhomogeneous superfluid system is expressed as a function of the order parameter $Φ({\mathbf{r}_{1}},{\mathbf{r}_{2}})$. It is shown that if the order parameter changes on macroscopic distances, the polarization charge ${{ρ}_{pol}}$ is proportional to $A{{\nabla }^{2}}n$, and the polarization $\mathbf{P}$ is proportional to $A\nabla n$, where $n$ is the density of the system. For noninteracting atoms the proportionality coefficient $A$ is independent of density, and in the presence of interaction $A$ is proportional to $n$. The change of the Bose gas density is found in the presence of a flow $\mathbf{w}={\mathbf{v}_{n}}-{\mathbf{v}_{s}}$ passing the vortex. It is found that a vortex in a superfluid film creates an electric potential above the film. This potential has the form of a potential of a dipole, allowing to assign a dipole moment to the vortex. The dipole moment is a sum of two terms, the first one is proportional to the relative flow velocity $\mathbf{w}$ and the second one is proportional to $\left[ \mathbf{κ}\times \mathbf{w} \right]$, where $\mathbf{κ}$ is the vortex circulation.

cond-mat.other↗

arXiv2015

Possible new electric effect in superfluid systems

We predict that propagation of third sound in a superfluid film creates an electric field in the surrounding area that can be observable with modern measurement devices when there are many vortex pairs in the system (e. g. in the vicinity of the superfluid transition temperature).

cond-mat.other↗

arXiv2011

Electric fields generated by quantized vortices

It is shown that in a magnetic field quantized vortices in a superfluid obtain a real quantized electric charge concentrated in the vortex core. This charge is compensated by an opposite surface charge located at a macroscopic distance from the vortex axis. It is determined that the polarization caused by the vortex velocity field does not give rise to electric fields outside an infinite cylinder. Observation of electric fields created by the vortices is possible only near the end surfaces of the cylinder which must be closed with dielectric covers to prevent superfluid leaking. Influence of cover properties on the potential created by the vortex is researched. Potential created by the vortices on point and ring electrodes are calculated.

cond-mat.other↗

arXiv2011

Superfluidity of electron-hole pairs in randomly inhomogeneous bilayer systems

In bilayer systems electron-hole (e-h) pairs with spatially separated components (i.e., with electrons in one layer and holes in the other) can be condensed to a superfluid state when the temperature is lowered. This article deals with the influence of randomly distributed inhomogeneities on the superfluid properties of such bilayer systems in a strong perpendicular magnetic field. Ionized impurities and roughenings of the conducting layers are shown to decrease the superfluid current density of the e-h pairs. When the interlayer distance is smaller than or close to the magnetic length, the fluctuations of the interlayer distance considerably reduce the superfluid transition temperature.

cond-mat.mes-hall↗

arXiv2010

Transport properties of ν=1 quantum Hall bilayers. Phenomenological description

We propose a phenomenological model that describes counterflow and drag experiments with quantum Hall bilayers in a ν_T=1 state. We consider the system consisting of statistically distributed areas with local total filling factors ν_{T1}>1 and ν_{T2}<1. The excess or deficit of electrons in a given area results in an appearance of vortex excitations. The vortices in quantum Hall bilayers are charged. They are responsible for a decay of the exciton supercurrent, and, at the same time, contribute to the conductivity directly. The experimental temperature dependence of the counterflow and drive resistivities is described under accounting viscous forces applied to vortices that are the exponentially increase functions of the inverse temperature. The presence of defect areas where the interlayer phase coherence is destroyed completely can result in an essential negative longitudinal drag resistivity as well as in a counterflow Hall resistivity.

cond-mat.str-el↗

arXiv2009

Relaxation of superflow in a network: an application to the dislocation model of supersolidity of helium crystals

We have considered the dislocation network model for the supersolid state in He-4 crystals. In difference with uniform 2D and 3D systems, the temperature of superfluid transition T_c in the network is much smaller than the degeneracy temperature T_d. It is shown that a crossover into a quasi superfluid state occurs in the temperature interval between T_c and T_d. Below the crossover temperature the time of decay of the flow increases exponentially under decrease of the temperature. The crossover has a continuous character and the crossover temperature does not depend on the density of dislocations.

cond-mat.quant-gas↗

arXiv2009

On the electric activity of superfluid systems

The Keldysh's theory of superfluidity of rarefied electron-hole gas is generalized to a case of possible pair polarizability. It was shown that inhomogeneity of the system leads to dipole moment which is proportional to the density gradient. The dipole moment appears also near boundaries of the system. It was determined that quantized vortices in a magnetic field carry a real electric charge. In He II at H=10 T and helium rotation velocity $10^2$ s$^{-1}$ the charge density is about $10^4e$ cm$^{-3}$, where $e$ is the electron charge.

cond-mat.supr-con↗