arXiv subjects

A. A. Kopasov

Publications and source records attributed to A. A. Kopasov.

9 recordsLinked to original sources

arXiv2026

Impurity-induced Inverse Faraday Effect

We provide a quantum-mechanical description of the photoinduced dc current states and magnetic fields around nonmagnetic point impurities in a two-dimensional (2D) electron gas irradiated by a circularly polarized electromagnetic wave. Based on the solution of the corresponding time-dependent Schrodinger equation within the second-order perturbation theory in the electromagnetic wave amplitude we find that the resulting dc magnetic field component perpendicular to the plane of the 2D system is distributed like in a set of random magnetic fluxes bound to the positions of impurities. As a result, the spatially averaged dc magnetic field does not vanish far from the sample edges and, thus, our scenario of the inverse Faraday effect in disordered systems differs strongly from the standard one based on the relaxation time approximation within the hydrodynamic or kinetic equation approaches which would give only the photoinduced currents flowing along the sample edges. The predicted mechanism for formation of rectified currents flowing around the impurity centers is shown to be generic both for 2D and three-dimensional systems. The internal dc magnetic field can give rise to the photoinduced Hall effect and Faraday rotation for a probing electromagnetic signal.

cond-mat.mes-hall↗

arXiv2026

Strongly nonlinear regime of Josephson transmission lines revealed by two-tone spectroscopy

We present experimental and theoretical studies of the off-resonant and strongly nonlinear regime of Josephson transmission lines (JTLs) with galvanically-coupled nonlinear elements. The transition from the weakly to the strongly nonlinear regime of a JTL induced by increasing the input power of the pump is probed via two-tone spectroscopy. Measurements of the phase of the transmission coefficient for a weak probe signal reveal a large increase and pronounced oscillations in the phase length variation as a function of the microwave power of the pump. Experimental observations are explained on the basis of the developed theoretical approach suitable for the description of the nonlinear response of strongly driven JTLs. Using the derived nonlinear wave equation, we show that the behavior of the phase length variation is associated with the oscillatory dependence of the Josephson inductances on the microwave power. It is demonstrated that the dissipation-induced propagation losses increase in the strongly nonlinear regime and also lead to smearing out the phase length oscillations. The developed theoretical analysis is in good agreement with experimental observations.

cond-mat.supr-con↗

arXiv2025

Interplay of ferroelectricity and interlayer superconductivity in van der Waals bilayers

We study the distinctive features of the interplay between the interlayer superconductivity and ferroelectricity in van der Waals heterostructures. Corresponding analysis is carried out within the framework of the quasiclassical Eilenberger equations for a tunnel coupled bilayer with inhomogeneous relative shift of the conduction bands between the layers, which describes the net charge transfer in sliding ferroelectrics. It is shown that the critical temperature of the interlayer superconductivity can be significantly enhanced for superconducting nuclei localized in the vicinity of ferroelectric domain walls. We demonstrate that the increase in the tunneling amplitude leads to the decrease (increase) in the difference between the critical temperatures for localized and homogeneous superconducting states for the spin-singlet (spin-triplet) interlayer superconductivity. We also perform an extensive analysis of the effects of the in-plane magnetic field on the interlayer superconductivity. It is shown that the orbital effect can result in the suppression of the spin-singlet interlayer superconductivity and to the enhancement of the spin-triplet one. We find that possible manifestations of the paramagnetic effect include the suppression of the interlayer superconductivity by rather weak Zeeman fields, the two-fold anisotropy of the critical magnetic field for the spin-triplet states as well as the appearance of the reentrant superconducting phases. It is shown that the joint influence of the orbital and paramagnetic mechanisms on the spin-triplet interlayer superconductivity can even lead to a nonmonotonic behavior of the superconducting critical temperature as a function of the external magnetic field. The obtained results are discussed in the context of recent experimental data on van der Waals structures with coexisting superconductivity and sliding ferroelectricity.

cond-mat.supr-con↗

arXiv2025

Proximity Induced Non-collinear Magnetic States in Planar Superconductor/Ferromagnet Hybrids

The proximity induced superconducting (S) correlations in ferromagnetic (F) layers of planar S/F hybrids are shown to be responsible for the appearance of a nonlinear interaction between the magnetic moments of the F layers. This interaction originates from the combined influence of the orbital and exchange phenomena and can result in the spontaneous formation of non-collinear magnetic states in these systems. The proposed nonlinear coupling mechanism and resulting changes of magnetic textures are crucial for the design of the superconducting spintronics devices exploiting the long-range spin triplet proximity effect.

cond-mat.supr-con↗

arXiv2023

Unconventional superconductivity and paramagnetic Meissner response triggered by nonlocal pairing interaction in proximitized heterostructures

Proximity phenomena and induced superconducting correlations in heterostructures are shown to be strongly affected by the nonlocal nature of the electronic attraction. The latter can trigger the formation of Cooper pairs consisting of electrons localized in neighbouring layers even in the absence of direct quasiparticle transfer between the layers. We investigate the manifestations of such nonlocal pairing and resulting unconventional induced superconductivity in an exemplary two-dimensional (2D) electronic system coupled to a conventional superconductor. The interplay between the quasiparticle tunneling and spin-triplet interlayer pairing is shown to generate the odd-frequency superconducting correlations in the 2D material which give rise to the paramagnetic contribution to the Meissner response and affect the energy resolved quasiparticle density of states. Experimental evidence for the above nonlocal interface pairing would provide new perspectives in engineering the unconventional superconducting correlations in heterostructures.

cond-mat.supr-con↗

arXiv2023

Adiabatic phase pumping in S/F/S hybrids with non-coplanar magnetization

We study the distinctive features of the phase pumping effect in Josephson transport through a three-layered ferromagnet F$_1$/F/F$_2$ with non-coplanar magnetization. Using Gor'kov and Bogoliubov-de Gennes formalisms we go beyond the quasiclassical approximation and analyze the dependence of the spontaneous Josephson phase $ψ$ on the exchange field $h$ in the F layer and details of magnetization profile. The pumping of the Josephson phase can be generated by the mutual rotation of magnetizations in F$_1$ and F$_2$ layers resulting in the nontrivial phase gain at the rotation period (Berry phase). The increase in $h$ is shown to cause changes in the topology of the phase evolution: the gain of the Josephson phase at the pumping period switches from $0$ to $2π$. We study the scenario of these switchings originating from the interplay between several competing local minima of the free energy of the junction versus the superconducting phase difference. Our analysis provides the basis for the search of experimental setup realizing the phase pumping phenomenon.

cond-mat.supr-con↗

arXiv2022

Disorder-induced trapping and anti-trapping of vortices in type-II superconductors

We study the features of the superconductivity nucleation and vortex configurations in superconductors with modulated disorder. Using the Ginzburg-Landau-type theory with spatially varying diffusion coefficient, we uncover and explain the switching between the vortex-defect attraction to the repulsion upon the increase in the external magnetic field. It is shown that for rather weak applied magnetic fields, a superconducting nucleus localized near the region with the suppressed diffusion coefficient possesses a nonzero vorticity whereas the increase in the magnetic field can lead to a transition into the state with zero winding number. We demonstrate the manifestations of this switching phenomenon in superconductors with a large number of defects by performing numerical simulations of the vortex structures in superconductors with periodic spatial profiles of the diffusion coefficient. The obtained results clarify the physics of the vortex arrangement in several classes of the superconducting materials including one-dimensional superlattices and nanopatterned superconductors with regular arrays of the defects characterized by the increased concentration of nonmagnetic impurities.

cond-mat.supr-con↗

arXiv2021

Geometry controlled superconducting diode and anomalous Josephson effect triggered by the topological phase transition in curved proximitized nanowires

We study the key features of the Josephson transport through a curved semiconducting nanowire. Based on numerical simulations and analytical estimates within the framework of the Bogoliubov-de Gennes equations we find the ground-state phase difference $φ_0$ between the superconducting leads tuned by the spin splitting field $h$ driving the system from the topologically trivial to the nontrivial superconducting state. The phase $φ_0$ vanishes for rather small $h$, grows in a certain field range around the topological transition, and then saturates at large $h$ in the Kitaev regime. Both the subgap and the continuum quasiparticle levels are responsible for the above behavior of the anomalous Josephson phase. It is demonstrated that the crossover region on $φ_0(h)$ dependencies reveals itself in the superconducting diode effect. The resulting tunable phase battery can be used as a probe of topological transitions in Majorana networks and can become a useful element of various quantum computation devices.

cond-mat.mes-hall↗

arXiv2020

Multiple topological transitions driven by the interplay of normal scattering and Andreev scattering

The effect of multiple topological transitions for electron-hole excitations is discovered in full shell proximitized semiconducting nanowires with trapped superconducting vortices, recently shown to be a promising platform for the realization of Majorana states at moderate longitudinal magnetic fields. The mechanism of such multiple transitions is uncovered and explained to be governed by the interplay of normal and Andreev reflections from the shell and by the textured spin-orbit coupling inside the semiconductor. The extensive analysis of emerging propagating and Majorana-type evanescent quasiparticle modes in such Andreev waveguides is performed. Experimentally, these modes reveal themselves in peculiarities of charge and spin-polarized heat transport.

cond-mat.mes-hall↗