arXiv subjects

Yu. S. Barash

Publications and source records attributed to Yu. S. Barash.

At least 19 recordsLinked to original sources

arXiv2026

Casimir-Lifshitz interaction between bodies integrated in a microelectromechanical/nanoelectromechanical quantum damped oscillator

A theory is proposed for the component of the Casimir-like force that arises between bodies embedded in a macroscopic quantum damped oscillator. When the oscillator's parameters depend on the distance between the bodies, the oscillator-induced Casimir-like force is generally determined by a broad spectral range extending to high frequencies, limited by the frequency dispersion of the damping function. Here it is shown that there is a large class of systems in which the low-frequency range dominates the forces. This allows for the use of the Ohmic approximation, which is crucial for extending the theory to the lumped element description of fluctuation-induced forces in electrical circuits. Estimates of the circuit-induced Casimir-Lifshitz force suggest that under certain conditions it can be identified experimentally due to its dependence on various circuit elements.

quant-ph↗

arXiv2026

Josephson diode and spin-valve effects on the surface of altermagnet CrSb

We experimentally investigate charge transport in In-CrSb and In-CrSb-In proximity devices, which are formed as junctions between superconducting indium leads and thick single crystal flakes of altermagnet CrSb. For double In-CrSb-In junctions, $dV/dI(B)$ curves are mirrored in respect to zero field for two magnetic field sweep directions, which is characteristic behavior of a Josephson spin valve. Also, we demonstrate Josephson diode effect by direct measurement of the critical current for two opposite directions in external magnetic field. We interpret these observations as a joint effect of the spin-polarized topological surface states and the altermagnetic spin splitting of the bulk bands in CrSb. For a single In-CrSb interface, the superconducting gap oscillates in magnetic field for both field orientations, which strongly resembles the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) behavior. FFLO is based on finite-momentum Cooper pairing, therefore, it is fully compatible with the requirements for the Josephson diode effect.

cond-mat.mes-hall↗

arXiv2024

Andreev reflection for MnTe altermagnet candidate

We experimentally study electron transport across a single planar junction between the indium electrode and MnTe altermagnet candidate. We confirm standard Ohmic behavior with strictly linear current-voltage curves above the indium critical field or temperature, although with high, about 100~kOhm, junction resistance. At low temperatures and in zero magnetic field, we observe a well-developed Andreev curve with the pronounced coherence peaks, which cannot be normally expected for these high values of normal junction resistance. The conclusion on the Andreev reflection is also supported by suppression in magnetic field, as well as by universality of the observed behavior for all of the investigated samples. The experimental results can be explained by specifics of Andreev transport through the disordered region at the superconductor-altermagnet interface. Due to a different set of restrictions on the possibility of Andreev reflection, an altermagnet suffers from the presence of disorder less than a normal spin-degenerate metal, so the conductance enhancement is retained throughout the superconducting gap.

cond-mat.mes-hall↗

arXiv2023

Reentrant proximity-induced superconductivity for GeTe semimetal

We experimentally investigate charge transport in In-GeTe and In-GeTe-In proximity devices, which are formed as junctions between superconducting indium leads and thick single crystal flakes of $α$-GeTe topological semimetal. We observe nonmonotonic effects of the applied external magnetic field, including reentrant superconductivity in In-GeTe-In Josephson junctions: supercurrent reappears at some finite magnetic field. For a single In-GeTe Andreev junction, the superconducting gap is partially suppressed in zero magnetic field, while the gap is increased nearly to the bulk value for some finite field before its full suppression. We discuss possible reasons for the results obtained, taking into account spin polarization of Fermi arc surface states in topological semimetal $α$-GeTe with a strong spin-orbit coupling. In particular, the zero-field surface state spin polarization partially suppresses the superconductivity, while it is recovered due to the modified spin-split surface state configuration in finite fields. As an alternative possible scenario, the transition into the Fulde-Ferrell-Larkin-Ovchinnikov state is discussed. However, the role of strong spin-orbit coupling in forming the nonmonotonic behavior has not been analyzed for heterostructures in the Fulde-Ferrell-Larkin-Ovchinnikov state, which is crucial for junctions involving GeTe topological semimetal.

cond-mat.mes-hall↗

arXiv2022

Boundary conditions for the order parameter and the proximity influenced internal phase differences in double superconducting junctions

This paper gives an overview of the unconventional dependence of internal phase differences on the external phase difference in superconductor-normal metal-superconductor (SINIS) and superconductor-superconductor-superconductor (SISIS) tunnel double junctions. The results are obtained within the Ginzburg-Landau (GL) approach that includes boundary conditions for the superconductor order parameter in the presence of a Josephson coupling through interfaces. The boundary conditions are derived within the GL theory and substantiated microscopically. The absence of the one-to-one correspondence between external $ϕ$ and internal $χ_{1,2}$ phase differences in the junctions is shown to occur in two qualitatively different ways, both of which result in the range of $χ_{1,2}$ reduced and prevent the $4π$-periodic current-phase relation $j=j_c\sin\fracϕ{2}$. In SINIS junctions, the effect of the supercurrent-induced phase incursion $φ$ between the end faces of the central electrode of mesoscopic length $L$ can play a crucial role. In SISIS junctions, there occurs the regime of interchanging modes, which is modified as $L$ decreases. The proximity and pair breaking effects in the double junctions with closely spaced interfaces are addressed.

cond-mat.supr-con↗

arXiv2021

Josephson spin-valve realization in the magnetic nodal-line topological semimetal Fe$_3$GeTe$_2$

Three-dimensional van der Waals ferromagnet Fe$_3$GeTe$_2$ (FGT) is regarded as a candidate for the magnetic topological nodal line semimetal. We investigate lateral electron transport between two 3~$μ$m spaced superconducting In leads beneath a thick three-dimensional FGT exfoliated flake. At low 30~mK temperature, we observe Josephson supercurrent that exhibits unusual critical current $I_c$ suppression by the magnetic field $B$. The overall $I_c(B)$ pattern is asymmetric in respect to the B sign. We demonstrate, that the asymmetry is defined by the magnetic field sweep direction, so the $I_c(B)$ pattern is strictly reversed (as $B$ to $-B$ inversion) for the opposite sweeps. We also observe an interplay between maximum and minimum in $I_c(B)$ in normal magnetic fields, while there are fast aperiodic $I_c(B)$ fluctuations for the in-plane ones. These effects can not be expected for homogeneous superconductor-ferromagnet-superconductor junctions, while they are known for Josephson spin valves. The mostly possible scenario for Josephson spin valve realization in FGT is the misalignment of spin polarizations of the Fermi arc surface states and ferromagnetic FGT bulk, but we also discuss possible influence of spin-dependent transport between magnetic domains.

cond-mat.mes-hall↗

arXiv2021

Coalescence of Andreev bound states on the surface of a chiral topological semimetal

We experimentally investigate the magnetic field dependence of Andreev transport through a region of proximity-induced superconductivity in CoSi topological chiral semimetal. With increasing parallel to the CoSi surface magnetic field, the sharp subgap peaks, associated with Andreev bound states, move together to nearly-zero bias position, while there is only monotonous peaks suppression for normal to the surface fields. The zero-bias $dV/dI$ resistance value is perfectly stable with changing the in-plane magnetic field. As the effects are qualitatively similar for In and Nb superconducting leads, they reflect the properties of proximized CoSi surface. The Andreev states coalescence and stability of the zero-bias $dV/dI$ value with increasing in-plane magnetic field are interpreted as the joined effect of the strong SOC and the Zeeman interaction, known for proximized semiconductor nanowires. We associate the observed magnetic field anisotropy with the recently predicted in-plane polarized spin texture of the Fermi arcs surface states.

cond-mat.mes-hall↗

arXiv2021

Damped oscillators within the general theory of Casimir and van der Waals forces

It is demonstrated that the general theory of Casimir and van der Waals forces describes the interaction-induced equilibrium thermodynamic potentials of the damped harmonic oscillator bilinearly coupled to the environment. An extended model for a damped oscillator is suggested along the lines of the general theory of Casimir and van der Waals forces, and the corresponding thermodynamic quantities obtained. While the original model involves a heat bath consisting of a large number of free oscillators having infinitesimal damping functions, the extended model allows any generally admissible frequency and temperature dependent dissipative susceptibilities of the heat bath constituents, influenced by the additional dissipative environmental channels that are not directly linked to the system oscillator. Consequently, the results obtained are applicable to the frequency and temperature dependent damping function of the system oscillator.

cond-mat.stat-mech↗

arXiv2020

Magnetically stable zero-bias anomaly in Andreev contact to the magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$

Being encouraged by the interplay between topology, superconductivity and magnetism, we experimentally investigate charge transport through the interface between the Nb superconductor and the time-reversal symmetry breaking Weyl semimetal Co$_3$Sn$_2$S$_2$. In addition to the proximity induced superconducting gap, we observe several subgap features, among which the most interesting is the prominent subgap zero-bias anomaly, absolutely stable against external magnetic fields up to the critical field of Nb. As the promising scenario for the zero-bias anomaly to appear in transport characteristics, we consider the proximity induced zero-energy Andreev bound states interfaced with the half-metallic Co$_3$Sn$_2$S$_2$ and influenced by the strong spin-orbit coupling and large Zeeman splitting.

cond-mat.mes-hall↗

arXiv2020

Lateral Josephson effect on the surface of Co$_3$Sn$_2$S$_2$ magnetic Weyl semimetal

We experimentally study lateral electron transport between two 5~$μ$m spaced superconducting indium leads on a top of magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$. For the disordered magnetic state of Co$_3$Sn$_2$S$_2$ crystal, we only observe the Andreev reflection in the proximity of each of the leads, which is indicative of highly transparent In-Co$_3$Sn$_2$S$_2$ interfaces. If the sample is homogeneously magnetized, it demonstrates well-developed anomalous Hall effect state. In this regime we find the Josephson current that takes place even for 5~$μ$m long junctions and shows the unusual magnetic field and temperature dependencies. As a possible reason for the results obtained, we discuss the contribution to the proximity-induced spin-triplet Josephson current from the topologically protected Fermi-arc states on the surface of Co$_3$Sn$_2$S$_2$.

cond-mat.mes-hall↗

arXiv2019

Phase relations in superconductor-normal metal-superconductor tunnel junctions

The phase difference $ϕ$, between the superconducting terminals in superconductor-normal metal-superconductor tunnel junctions (SINIS), incorporates the phase differences $χ_{1,2}$ across thin interfaces of constituent $SIN$ junctions and the phase incursion $φ$ between the side faces of the central electrode of length $L$. It is demonstrated here that $χ_{1,2}$ pass through over their proximity-reduced domain twice, there and back, while $ϕ$ changes over the single period. Two corresponding solutions, that describe the double-valued order-parameter dependence on $χ_{1,2}$, jointly form the single-valued dependence on $ϕ$, operating in two adjoining regions of $ϕ$. The phase incursion $φ$ plays a crucial role in creating such a behavior. The current-phase relation $j(ϕ,L)$ is composed of the two solutions and, at a fixed small $L$, is characterized by the phase-dependent effective transmission coefficient.

cond-mat.supr-con↗

arXiv2018

Proximity-reduced range of internal phase differences in double Josephson junctions with closely spaced interfaces

A substantial influence of the proximity and pair breaking effects on the range of internal phase differences is shown to take place in symmetric double Josephson junctions with closely spaced interfaces and to affect the evolution of the supercurrent j with the changing central lead's length L. If the phase difference phi between the external leads is controlled and L exceeds a few coherence lengths, the regime of interchanging modes is established. The range of the phase differences across the two individual interfaces is reduced with decreasing L, and the states of the higher energy mode are gradually eliminated. With a further decrease of L the regime of interchanging modes is destroyed along with the asymmetric mode. The conventional single junction current-phase relation j(phi) is eventually established and the condensate states' doubling is fully removed at very small L.

cond-mat.supr-con↗

arXiv2017

Proximity-induced minimum radius of superconducting thin rings closed by the Josephson 0 or pi junction

Superconductivity is shown to be completely destroyed in thin mesoscopic or nanoscopic rings closed by the junction with a noticeable interfacial pair breaking and/or a Josephson coupling, if a ring's radius r is less than the minimum radius r_min. The quantity r_min depends on the phase difference across the junction, or on the magnetic flux that controls the phase difference in the flux-biased ring. It also depends on the Josephson and interfacial effective coupling constants, and in particular, on whether the ring is closed by 0 or pi junction. The current-phase relation is substantially modified when the ring's radius exceeds r_min for some of the phase difference values, or slightly goes beyond its maximum. The modified critical temperature Tc, as well as the temperature dependent supercurrent near Tc are identified here as functions of the ring's radius and the magnetic flux.

cond-mat.supr-con↗

arXiv2014

Magnetic penetration depth and vortex structure in anharmonic superconducting junctions with an interfacial pair breaking

The penetration depth l_j in superconducting junctions is identified within the Ginzburg-Landau theory as a function of the interfacial pair breaking, of the magnetic field and of the Josephson coupling strength. When the interfacial pair breaking goes up, l_j increases and an applicability of the local Josephson electrodynamics to junctions with a strong Josephson coupling is extended. In the junctions with strongly anharmonic current-phase relations, the magnetic field dependence of l_j is shown to lead to a significant difference between the weak-field penetration depth and the characteristic size of the Josephson vortex. For such junctions a nonmonotonic dependence of l_j and of the lower critical field on the Josephson coupling constant is found, and the specific features of spatial profiles of the supercurrent and the magnetic field in the Josephson vortex are established.

cond-mat.supr-con↗

arXiv2014

The magnetic penetration depth influenced by the proximity to the surface

The effect of smooth inhomogeneities near a superconductor boundary on the magnetic penetration depth $λ$ is studied with emphasis on the proximity-induced spatial dependence of the Cooper pair amplitude. The influence of surface pair breaking or pair formation on $λ$ is described within the Ginzburg-Landau theory, with no model assumptions, for both strongly type-II and strongly type-I homogeneous superconductors. Generic values of $λ$, which can differ greatly from the London penetration depth, are identified and demonstrated to be induced by large-scale inhomogeneities, when superconductivity is strongly suppressed on the surface.

cond-mat.supr-con↗

arXiv2012

Non-Fraunhofer patterns of the anharmonic Josephson current influenced by a strong interfacial pair breaking

In the junctions with a strong Josephson coupling and a pronounced interfacial pair breaking, the magnetic interference patterns of the Josephson current are shown to differ substantially from the standard Fraunhofer shape. The Fraunhofer pattern occurs, when Josephson couplings are weak. The narrow peak of the critical current, centered at the zero magnetic field, and the suppressed hills at finite field values are the characteristic features of the non-Fraunhofer magnetic field modulation of the critical current, obtained in this paper.

cond-mat.supr-con↗

arXiv2012

Probing interfacial pair breaking in tunnel junctions based on the first and the second harmonics of the Josephson current

It will be shown that a pronounced interfacial pair breaking can be identified in Josephson tunnel junctions provided the first j_{1c} and the second j_{2c} harmonics of the supercurrent, as well as the depairing current in the bulk j_{dp}, are known. Namely, within the Ginzburg-Landau theory a strong interfacial pair breaking results in the relation j_{2c}j_{dp}>>j_{1c}^2, while in standard junctions, with negligibly small pair breaking, the relation of opposite character takes place.

cond-mat.supr-con↗

arXiv2012

Anharmonic Josephson current in junctions with an interface pair breaking

Planar superconducting junctions with a large effective Josephson coupling constant and a pronounced interface pair breaking are shown to represent weak links with small critical currents and strongly anharmonic current-phase relations. The supercurrent near Tc is described taking into account the interface pair breaking as well as the current depairing and the Josephson coupling-induced pair breaking of arbitrary strengths. A new analytical expression for the anharmonic supercurrent, which is in excellent agreement with the numerical data presented, is obtained. In junctions with a large effective Josephson coupling constant and a pronounced interface pair breaking, the current-induced depairing is substantially enhanced in the vicinity of the interface thus having a crucial influence on the current-phase relation despite a small depairing in the bulk.

cond-mat.supr-con↗