arXiv subjects

A. V. Andreev

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

At least 19 recordsLinked to original sources

arXiv2026

Electromotive entrainment of charge and heat currents in graphene

We develop a hydrodynamic theory of charge and heat currents induced by traveling waves, such as surface acoustic waves, in graphene devices near charge neutrality. The currents depend on the intrinsic conductivity and viscosity of the electron liquid, the disorder strength, and the geometry of the device. We obtain analytic expressions for the heat and charge currents to second order in the wave amplitude for Hall-bar devices. At charge neutrality and in the absence of DC bias, the heat content is entrained by the wave in the absence of net charge transfer. At the same time, device conductance is enhanced by the wave. Away from charge neutrality, the transport charge current induced by the wave arises in the absence of a DC bias.

cond-mat.mes-hall↗

arXiv2026

Fluctuation-induced giant magnetoresistance in charge-neutral graphene

The Johnson-Nyquist noise associated with the intrinsic conductivity of the electron liquid, induces fluctuations of the electron density in charge-neutral graphene devices. In the presence of external electric and magnetic fields, the fluctuations of charge density and electric current induce a fluctuating hydrodynamic flow. We show that the resulting advection of charge produces a fluctuation contribution to the macroscopic conductivity of the system, $σ_{\mathrm{fl}}$, and develop a quantitative theory of $σ_{\mathrm{fl}}$. At zero magnetic field, $σ_{\mathrm{fl}}$ diverges logarithmically with the system size and becomes rapidly suppressed at relatively small fields. This results in giant magnetoresistance of the system.

cond-mat.mes-hall↗

arXiv2026

Nonreciprocity of hydrodynamic electron transport in noncentrosymmetric conductors

We show that the nonreciprocity of hydrodynamic electron transport in noncentrosymmetric conductors with broken time-reversal symmetry (TRS) is significantly enhanced compared to the disorder-dominated regime. This enhancement is caused by the linear dependence of the viscosity of the electron liquid on the flow velocity, which is allowed in the absence of TRS and Galilean invariance. The resulting nonlinear flows break dynamical similarity and must be characterized by two dimensionless parameters: the Reynolds number and the emergent nonreciprocity number. The latter is linear in velocity but independent of system size. We determine the nonlinear conductance of a Hall bar and show that the nonreciprocal correction to the current can be of comparable magnitude to its reciprocal counterpart.

cond-mat.mes-hall↗

arXiv2025

Dragging of electric current by hydrodynamic flow at charge neutrality

We develop a theory of drag in graphene double layers near charge neutrality. We work in the regime of electron hydrodynamics and account for interlayer correlations of charge puddle disorder. The drag resistivity is expressed in terms of the viscosity, intrinsic conductivity of the electron liquid, and the correlation function of the puddle disorder. The contributions of the interlayer transfer of momentum and energy to drag have opposite signs. This leads to a nonmonotonic dependence of the drag resistivity on the carrier density. For layer-symmetric doping, the drag resistivity changes sign as a function of the carrier density. At interlayer separations shorter than the disorder correlation length, the transconductivity saturates to the disorder-induced enhancement of the intralayer conductivity. We provide quantitative estimates of the effect for Dirac electron liquids in monolayer graphene and bilayer graphene double-layer devices.

cond-mat.mes-hall↗

arXiv2025

Photogalvanic effect in hydrodynamic flows of nonreciprocal electron liquids

We study nonlinear hydrodynamic electron transport driven by an AC electric field. In noncentrosymmetric conductors with broken time-reversal (TR) symmetry the nonlinear flow of such liquids is nonreciprocal, giving rise to a DC current $I^{DC}$ that is quadratic in the amplitude of the AC electric field. This is the hydrodynamic analogue of the linear photogalvanic effect (PGE), which arises in bulk noncentrosymmetric materials with broken TR symmetry. The magnitude of $I^{DC}$ depends on both the properties of the electron fluid and the geometry of the flow, and may be characterized by two dimensionless parameters: the nonreciprocity number $\mathcal{N}$, and the frequency-dependent vibrational number $\mathcal{R}$. Due to nonlocality of hydrodynamic transport, at low frequencies of the AC drive, $I^{DC}$ is super-extensive. The AC component of the electric current is likewise strongly affected by nonreciprocity: the hysteretic current-voltage dependence becomes skewed, which can be interpreted in terms of nonreciprocity of the memory retention time.

cond-mat.mes-hall↗

arXiv2025

Measurement of the differential and total cross-sections of $γ$-ray emission induced by $14.1$ MeV neutrons for C, Al, Si, Ca, Ti, Cr, and Fe using the tagged neutron method

In this work, differential cross sections of $γ$-ray emission produced in nuclear reactions induced by $14.1$~MeV neutrons are measured for the $4.439$~MeV line from carbon, as well as for $10$ individual $γ$-ray lines from aluminum, $6$ from silicon, $8$ from calcium, $16$ from titanium, $6$ from chromium, and $14$ from iron. The measurements were conducted using the tagged neutron method with four LaBr$_3$(Ce) scintillation detectors positioned at angles of $25^{\circ}$, $45^{\circ}$, $60^{\circ}$, and $70^{\circ}$ relative to the generator target -- sample center axis. A neutron generator capable of producing $16$ separate beams of tagged neutrons was employed, which, combined with the detector system, enabled the determination of differential cross-sections for $64$ distinct angle values in the range of $17^{\circ}$ to $89^{\circ}$. To simplify data visualization, the angular distributions were divided into $5^{\circ}$ intervals, with weighted mean values of the angle and differential cross-section calculated for each interval. Corrections for multiple neutron scattering and attenuation, $γ$-ray attenuation, and total detection efficiency, computed using GEANT4, were accounted for in the cross-section calculations. Additional measurements were performed to validate the correction calculations. The total $γ$-ray emission cross-sections were obtained by approximating the angular distributions with even-order Legendre polynomial expansions up to the $6$th degree, followed by integration over the full solid angle. The total systematic error for the obtained data was estimated as $9$\,\%.

nucl-ex↗

arXiv2025

Properties of two level systems in current-carrying superconductors

We show that in disordered superconductors, at sufficiently low frequencies $ω$, the coupling of TLS to external ac electric fields increases dramatically in the presence of a dc supercurrent. This giant enhancement manifests in all ac linear and nonlinear phenomena. In particular, it leads to a parametric enhancement of the real part of the ac conductivity and, consequently, of the equilibrium current fluctuations. If the distribution of TLS relaxation times is broad, the conductivity is inversely proportional to $ω$, and the spectrum of the equilibrium current fluctuations takes the form of 1/f noise.

cond-mat.supr-con↗

arXiv2024

Spin drag mechanism of giant thermal magnetoresistance

We study hydrodynamic thermal transport in high-mobility two-dimensional electron systems placed in an in-plane magnetic field, and identify a new mechanism of thermal magnetotransport. This mechanism is caused by drag between the electron populations with opposite spin polarization, which arises in the presence of a hydrodynamic flow of heat. In high mobility systems, spin drag results in strong thermal magnetoresistance, which becomes of the order of 100% at relatively small spin polarization of the electron liquid. We express the thermal magnetoresistance in terms of intrinsic dissipative coefficients of electron fluid and show that it is primarily determined by the spin diffusion constant.

cond-mat.mes-hall↗

arXiv2024

Giant microwave absorption in the vortex lattice in $s$-wave superconductors

In this article we study microwave absorption in superconductors in the presence of a vortex lattice. We show that in addition to the conventional absorption mechanism associated with the vortex core motion, there is another mechanism of microwave absorption, which is caused by the time-dependence of the quasiparticle density of states outside the vortex cores. This mechanism exists even in the absence of vortex motion and provides the dominant contribution to microwave absorption in a broad interval of physical parameters. At low frequencies, the dissipative part of the microwave conductivity $σ(ω)$ is proportional to the inelastic relaxation time, $τ_{\mathrm{in}}$, which is typically much larger than the elastic relaxation time, $τ_{\mathrm{el}}$. At high frequencies $σ(ω)$ is proportional to the quasiparticle diffusion time across the inter-vortex distance, $τ_{\mathrm D}$, which is still larger than $τ_{\mathrm{el}}$.

cond-mat.supr-con↗

arXiv2024

Giant magnetoresistance in weakly disordered non-Galilean invariant conductors

We develop a hydrodynamic description of electron magnetotransport in conductors without Galilean invariance in the presence of a weak long-range disorder potential. We show that magnetoresistance becomes strong (of order 100 %) at relatively small fields, at which the inverse square of the magnetic length becomes comparable to disorder-induced variations of the electron density. The mechanism responsible for this anomalously strong magnetoresistance can be traced to the appearance of magnetic friction force in liquids with nonvanishing intrinsic conductivity. We derive general results for the galvanomagnetic and thermomagnetic kinetic coefficients, and obtain their dependence on the intrinsic dissipative properties of the electron liquid and the correlation function of the disorder potential. We apply this theory to graphene close to charge neutrality and cover the crossover to a high-density regime.

cond-mat.mes-hall↗

arXiv2023

Measurement of yields and angular distributions of $γ$-quanta from the interaction of $14.1$ MeV neutrons with oxygen, phosphorus and sulfur

A study of the inelastic scattering of neutrons with an energy of $14.1$~MeV on the nuclei of oxygen, phosphorus and sulfur was carried out at the TANGRA facility at JINR (Dubna). The purpose of the experiment was to refine existing and obtain new data on the yields and angular distributions of $γ$-quanta emitted by the studied nuclei as a result of neutron-induced nuclear reactions using the tagged neutron method. Two types of detector systems were used to register $γ$-quanta. The $γ$-ray yields were measured using a high-purity germanium (HPGe) detector. The angular distributions of $γ$-rays were obtained using a system of 18 scintillation detectors based on bismuth germanite Bi$_{4}$Ge$_{3}$O$_{12}$ (BGO) located around the sample. As a result of the studies carried out, the yields of two transitions for the reaction of tagged neutrons with $^{16}$O, nine transitions for the reaction with $^{31}$P, and nine transitions for the reaction with $^{32}$S were measured for the first time. The angular anisotropy of the $γ$-radiation accompanying the inelastic scattering of neutrons with an energy of $14.1$~MeV on $^{31}$P nuclei was also measured for the first time.

nucl-ex↗

arXiv2023

Giant nonreciprocity of current-voltage characteristics of noncentrosymmetric supercondctor-normal metal-superconductor junctions

We develop a theory of nonreciprocal current-voltage (I-U) characteristics in noncentrosymmetric superconductor-normal metal-superconductor junctions. We show that at small voltages the nonreciprocal features of the I-U characteristics can be expressed entirely in terms of the dependence of the nonreciprocal part of the quasiparticle density of states in the normal metal part of the junction on the order parameter phase difference $χ$ across the junction. The amplitude of the nonreciprocity in this regime is proportional to the inelastic quasiparticle relaxation time $τ_{in}$, and can be much larger than that in normal materials, where it is proportional to the elastic relaxation time $τ_{el}$. At low bias the I-U characteristics possess additional symmetry, not present in normal conductors; they remain invariant under simultaneous reversal of current, voltage and the magnetic field.

cond-mat.supr-con↗

arXiv2023

Thermal transfer enhancement by hydrodynamic plasmons in electron bilayers

We develop a theory of heat transfer induced by thermal charge fluctuations in two-dimensional electron double layers. We consider pristine systems comprised of identical layers, and focus on the regime of sufficiently high temperatures and interlayer distances $d$, where the relevant charge fluctuations may be described using the hydrodynamic approach. In this limit heat transfer is dominated by the plasmon resonances. For systems with Galilean-invariant electron dispersion the interlayer thermal conductance $\varkappa$ is proportional to the kinematic viscosity of the electron liquid, and decreases as $1/d^4$. In the absence of Galilean invariance $\varkappa \propto σ/d^3$, where $σ$ is the intrinsic conductivity of the liquid. This strong enhancement can be traced to a drastically different broadening of plasmon resonances in systems with and without Galilean invariance.

cond-mat.mes-hall↗

arXiv2023

Hydrodynamics of thermally-driven chiral propulsion and separation

Considerable effort has been directed towards the characterization of chiral mesoscale structures, as shown in chiral protein assemblies and carbon nanotubes. Here, we establish a thermally-driven hydrodynamic description for the actuation and separation of mesoscale chiral structures in a fluid medium. Cross flow of a Newtonian liquid with a thermal gradient gives rise to chiral structure propulsion and separation according to their handedness. In turn, the chiral suspension alters the liquid flow which thus acquires a transverse (chiral) velocity component. Since observation of the predicted effects requires a low degree of sophistication, our work provides an efficient and inexpensive approach to test and calibrate chiral particle propulsion and separation strategies.

cond-mat.soft↗

arXiv2023

Negative critical currents in single-channel Josephson junctions

We argue that negative critical currents arise generically in Josephson junctions formed by single channel conductors. Specifically, we theoretically study the Josephson coupling between two superconducting leads connected by a one-dimensional conductor in the Coulomb blockade regime. We show that in the clean regime the sign of the critical current alternates with the number of electrons in the normal region. For odd occupancy the critical current is negative even when the number of electrons on the conductor is large.

cond-mat.supr-con↗

arXiv2022

Current-voltage characteristics of superconductor-normal metal-superconductor junctions

We develop a theory of current-voltage (I-U) characteristics for superconductor-normal metal-superconductor (SNS) junctions. At small voltages and sufficiently low temperatures the I-U characteristics of the junction is controlled by the inelastic relaxation time, τ_{in}. In particular, the linear conductance is proportional to, τ_{in}. In this regime the I-U characteristics can be expressed solely in terms of dependence of the density of states in the normal region, ν(χ), on the phase difference of the order parameter across the the junction. In contrast, at large voltages the I-U characteristics of the device is controlled by the elastic relaxation time, τ_{el}, which is much smaller than the inelastic one.

cond-mat.supr-con↗

arXiv2022

Microwave response of type-II superconductors at weak pinning

Theory of linear microwave response of thin films of type-II superconductors in the mixed state is developed taking into account random spatial fluctuations of the parameters of the system, such as the order parameter, diffusion coefficient, or film thickness. In the regime of collective pinning the microwave response of the system exhibits strong frequency dispersion, arising from nonequilibrium vortex core quasiparticles. The corresponding contribution to the ac conductivity is controlled by the inelastic relaxation time, and may exceed the usual Bardeen-Stephen conductivity. It is caused by the Debye-type inelastic relaxation. Debye mechanism of microwave losses may be responsible for strong effects of electromagnetic noise upon dc conductivity in the mixed state at low temperatures.

cond-mat.supr-con↗

arXiv2022

$^{178}$Hg and asymmetric fission of neutron-deficient pre-actinides

Fission at low excitation energy is an ideal playground to probe the impact of nuclear structure on nuclear dynamics. While the importance of structural effects in the nascent fragments is well-established in the (trans-)actinide region, the observation of asymmetric fission in several neutron-deficient pre-actinides can be explained by various mechanisms. To deepen our insight into that puzzle, an innovative approach based on inverse kinematics and an enhanced version of the VAMOS++ heavy-ion spectrometer was implemented at the GANIL facility, Caen. Fission of $^{178}$Hg was induced by fusion of $^{124}$Xe and $^{54}$Fe. The two fragments were detected in coincidence using VAMOS++ supplemented with a new SEcond Detection arm. For the first time in the pre-actinide region, access to the pre-neutron mass and total kinetic energy distributions, and the simultaneous isotopic identification of one the fission fragment, was achieved. The present work describes the experimental approach, and discusses the pre-neutron observables in the context of an extended asymmetric-fission island located south-west of $^{208}Pb. A comparison with different models is performed, demonstrating the importance of this "new" asymmetric-fission island for elaborating on driving effects in fission.

nucl-ex↗