arXiv subjects

Sergey S. Pershoguba

Publications and source records attributed to Sergey S. Pershoguba.

At least 19 recordsLinked to original sources

arXiv2025

Topological Hall-like behavior of multidomain ferromagnets

We investigate the emergence of topological Hall-like (THE-like) signals in disordered multidomain ferromagnets. Non-monotonic behavior in Hall resistivity, commonly attributed to topological spin textures such as skyrmions, is produced in a random resistor network model without any chirality. It arises from simple mechanisms of the anomalous Hall effect (AHE) in combination with the domain wall scattering. By varying domain configurations and domain wall resistances, we explore the conditions under which the non-monotonic resistivity can be enhanced. Our results emphasize the need for careful analysis in distinguishing between true topological Hall effects and artifacts caused by domain disorders.

cond-mat.mes-hall↗

arXiv2024

Inertia in skyrmions confined to one-dimensional geometries

Magnetic skyrmions are conventionally attributed to having zero mass. In contrast, we show that skyrmions confined to one-dimensional geometries generically acquire mass (inertia) due to the combined effects of the skyrmion Hall effect and the elasticity of the system. We investigate the massive behavior of the skyrmion for a simplified periodic model of the disorder. We show that skyrmion mass lowers the critical depinning force and leads to a step-like behavior in the skyrmion velocity-vs-current curves, which were recently observed in experiments. Finite mass could also lead to hysteresis in the velocity-vs-current curves.

cond-mat.other↗

arXiv2022

Experimental observation of one-dimensional motion of interstitial skyrmion in FeGe

The interplay between dimensionality and topology manifests in magnetism via both exotic texture morphology and novel dynamics. A free magnetic skyrmion exhibits the skyrmion Hall effect under electric currents. Once it is confined in one-dimensional (1D) channels, the skyrmion Hall effect would be suppressed, and the current-driven skyrmion speed should be boosted by the non-adiabatic spin transfer torque \b{eta}. Here, we experimentally demonstrate that stripes of a spatially modulated spin helix serve as natural 1D channels to restrict skyrmion. Using FeGe as a benchmark, an interstitial skyrmion is created by geometry notch and further moves steadily without the skyrmion Hall effect. The slope of the current-velocity curve for 1D skyrmion is enhanced almost by an order of magnitude owing to a large \b{eta} in FeGe. This feature is also observed in other topological defects. Utilizing the 1D skyrmion dynamics would be a highly promising route to implement topological spintronic devices.

cond-mat.mes-hall↗

arXiv2022

Hall Effect Induced by Topologically Trivial Target Skyrmions

Electrons moving through a noncoplanar magnetic texture acquire a Berry phase, which can be described as an effective magnetic field. This effect is known as the topological Hall effect and has been observed in topological spin textures. Motivated by recent experimental realizations, here we study the Hall effect in a nontopological magnetic texture known as a target skyrmion. We start from a simplified semiclassical picture and show that the Hall signal is a nonmonotonic function of both the electronic energy and target skyrmion radius. That observation carries over to the fully quantum mechanical treatment in a Landauer-Büttiker formalism in a mesoscopic setting. Our conclusion challenges the popular opinion in the community that the Hall effect in such structures necessarily requires a nonzero skyrmion number.

cond-mat.mes-hall↗

arXiv2022

Direct current in a stirred optical lattice

We study how the energy dispersion of bosonic atoms loaded into an optical lattice becomes modified due to periodic circular stirring of the lattice to the second order in the strength of stirring. If the lattice breaks mirror symmetry, the bosonic atoms may acquire a nonzero group velocity at the center of the Brillouin zone and produce a nonzero direct current. This effect is similar to the circular photogalvanic effect in solid-state physics. It can be used to transport neutral bosonic atoms in an optical lattice over a given distance in an arbitrary direction. However, when the drive frequency is detuned to avoid resonant transitions with energy absorption, we argue that the induced current is not persistent, but transient. An experimental study of the induced current relaxation could give answers to perplexing questions about equilibrization in driven systems.

cond-mat.mes-hall↗

arXiv2022

Optical control of topological memory based on orbital magnetization

Under suitable conditions, some twisted graphene multilayers and transition-metal dichalcogenides become Chern insulators, exhibiting the anomalous quantum Hall effect and orbital magnetization due to spontaneous valley polarization. We study interaction of a Chern insulator with circularly polarized light. The interaction energy contains an antisymmetric term that couples to the helicity of incident light. For a two-band Chern insulator, this term is expressed as an integral involving the Berry curvature of the system. Taking advantage of this interaction, we propose an experimental protocol for switching topological memory based on orbital magnetization by circularly polarized light. Moreover, two laser beams of opposite circular polarization can nucleate domains of opposite magnetization and thus produce an optically configurable domain wall carrying topologically protected chiral edge modes.

cond-mat.mes-hall↗

arXiv2021

Electronic scattering off a magnetic hopfion

We study scattering of itinerant electrons off a magnetic hopfion in a three-dimensional metallic magnet described by a magnetization vector $\mathbf S(\mathbf r)$. A hopfion is a confined topological soliton of $\mathbf S(\mathbf r)$ characterized by an {\it emergent} magnetic field $B_γ(\mathbf r) \equiv ε_{αβγ} \,\mathbf S\cdot(\nabla_α\mathbf S\times \nabla_β\mathbf S)/4 \neq 0$ with vanishing average value $\langle \mathbf B(\mathbf r)\rangle = 0$. We evaluate the scattering amplitude in the opposite limits of large and small hopfion radius $R$ using the eikonal and Born approximations, respectively. In both limits, we find that the scattering cross-section contains a skew-scattering component giving rise to the Hall effect within a hopfion plane. That conclusion contests the popular notion that the topological Hall effect in non-collinear magnetic structures necessarily implies $\langle \mathbf B(\mathbf r)\rangle \neq 0$. In the limit of small hopfion radius $pR \ll 1$, we expand the Born series in powers of momentum $p$ and identify different expansion terms corresponding to the hopfion anisotropy, toroidal moment, and skew-scattering.

cond-mat.mes-hall↗

arXiv2020

Current distribution in a slit connecting two graphene half-planes

We investigate the joint effect of viscous and Ohmic dissipation on electric current flow through a slit in a barrier dividing a graphene sheet in two. In the case of the no-slip boundary condition, we find that the competition between the viscous and Ohmic types of the charge flow results in the evolution of the current density profile from a concave to convex shape. We provide a detailed analysis of the evolution and identify favorable conditions to observe it in experiment. In contrast, in the case of the no-stress boundary condition, there is no qualitative difference between the current profiles in the Ohmic and viscous limits. The dichotomy between the behavior corresponding to distinct boundary conditions could be tested experimentally.

cond-mat.mes-hall↗

arXiv2019

Landauer Formula for a Superconducting Quantum Point Contact

We generalize the Landauer formula to describe the dissipative electron transport through a superconducting point contact. The finite-temperature, linear-in-bias, dissipative DC conductance is expressed in terms of the phase- and energy-dependent scattering matrix of the Bogoliubov quasiparticles in the quantum point contact. The derived formula is also applicable to hybrid superconducting-normal structures and normal contacts, where it agrees with the known limits of Andreev reflection and normal-state conductance, respectively.

cond-mat.supr-con↗

arXiv2019

Thermopower and thermal conductance of a superconducting quantum point contact

We find the charge and heat currents caused by a temperature difference applied to a superconducting point contact or to a quantum point contact between a superconducting and normal conductors. The results are formulated in terms of the properties of the electron scattering matrix of the quantum point contact in its normal state, and are valid at any transmission coefficient. In the low-transmission limit, the new theory provides reliable results, setting the limits for the use of the popular method of tunnel Hamiltonian.

cond-mat.mes-hall↗

arXiv2018

Odd-frequency Pairing in Conventional Josephson Junctions

Using a simple theoretical model, we demonstrate the emergence of odd-frequency pair amplitudes in conventional Josephson junctions both in the absence of a voltage (DC effect) and in the presence of a finite voltage (AC effect). In both cases, we find that odd-frequency interlead pairing emerges whenever a Josephson current is expected to flow. Additionally, we show that the interlead spin-susceptibility is directly influenced by the presence of the odd-frequency pair amplitudes. Specifically, we find that the spin-susceptibility is suppressed when the odd-frequency component is the largest. By establishing a novel link between the physics of Josephson junctions and odd-frequency pairing, this work demonstrates the importance of odd-frequency pairing for understanding conventional superconducting systems.

cond-mat.supr-con↗

arXiv2017

Dirac magnons in honeycomb ferromagnets

The discovery of the Dirac electron dispersion in graphene led to the question of the Dirac cone stability with respect to interactions. Coulomb interactions between electrons were shown to induce a logarithmic renormalization of the Dirac dispersion. With a rapid expansion of the list of compounds and quasiparticle bands with linear band touching, the concept of bosonic Dirac materials has emerged. We consider a specific case of ferromagnets consisting of the Van der Waals-bonded stacks of honeycomb layers, e.g chromium trihalides CrX3 (X = F, Cl, Br and I), that display two spin wave modes with energy dispersion similar to that for the electrons in graphene. At the single particle level, these materials resemble their fermionic counterparts. However, how different particle statistics and interactions affect the stability of Dirac cones has yet to be determined. To address the role of interacting Dirac magnons, we expand the theory of ferromagnets beyond the standard Dyson theory to a case of non-Bravais honeycomb layers. We demonstrate that magnon-magnon interactions lead to a significant momentum-dependent renormalization of the bare band structure in addition to strongly momentum-dependent magnon lifetimes. We show that our theory qualitatively accounts for hitherto unexplained anomalies in a nearly half century old magnetic neutron scattering data for CrBr3. We also show that honeycomb ferromagnets display dispersive surface and edge states, unlike their electronic analogs.

cond-mat.mtrl-sci↗

arXiv2016

Skyrmion-induced bound states in a superconductor

We consider a superconductor proximity coupled to a two-dimensional ferromagnetic film with a skyrmion texture. Using the T-matrix calculations and numerical modeling we calculate the spin-polarized local density of states in the superconductor in the vicinity of the skyrmion. We predict the skyrmion bound states (SBS) that are induced in the superconductor, similar to the well-known Yu-Shiba-Rusinov (YSR) states. The SBS wavefunctions have spatial power law decay. Presence of the SBS suggests the mechanism by which superconductivity could facilitate an effective long-range interaction between skyrmions when their SBS wavefunctions overlap.

cond-mat.supr-con↗

arXiv2016

Skyrmion-induced subgap states in p-wave superconductors

In s-wave systems, it has been theoretically shown that a ferromagnetic film hosting a skyrmion can induce a bound state embedded in the opposite-spin continuum. In this work, we consider a case of skyrmion-induced state in a p-wave superconductor. We find that the skyrmion induces a bound state that generally resides \emph{within} the spectral gap and is isolated from all other states, in contrast to the case of conventional superconductors. To this end, we derive an approximate expression for the $T$-matrix, through which we calculate the spin-polarized local density of states which is observable in scanning tunneling microscopy measurements. We find the unique spectroscopic features of the skyrmion-induced bound state and discuss how our predictions could be employed as novel experimental probes for p-wave superconducting states.

cond-mat.mes-hall↗

arXiv2015

Currents induced by magnetic impurities in superconductors with spin-orbit coupling

We show that superconducting currents are generated around magnetic impurities and ferromagnetic islands proximity-coupled to superconductors with finite spin-orbit coupling. Using the Ginzburg-Landau theory, T-matrix calculation, as well as self-consistent numerical simulation on a lattice, we find a strong dependence of the current on the direction and magnitude of the magnetic moment. We establish that in the case of point magnetic impurities, the current is carried by the induced Yu-Shiba-Rusinov (YSR) subgap states. In the vicinity of the phase transition, where the YSR states cross at zero energy, the current increases dramatically. Furthermore, we show that the currents are orthogonal to the local spin polarization and, thus, can be probed by measuring the spin-polarized local density of states.

cond-mat.str-el↗

arXiv2015

Effects of a tilted magnetic field in a Dirac double layer

We calculate the energy spectrum of a Dirac double layer, where each layer has the Dirac electronic dispersion, in the presence of a tilted magnetic field and small interlayer tunneling. We show that the energy splitting between the Landau levels has an oscillatory dependence on the in-plane magnetic field and vanishes at a series of special tilt angles of the magnetic field. Using a semiclassical analysis, we show that these special tilt angles are determined by the Berry phase of the Dirac Hamiltonian. The interlayer tunneling conductance also exhibits an oscillatory dependence on the magnetic field tilt angle, known as the angular magnetoresistance oscillations (AMRO). Our results are applicable to graphene double layers and thin films of topological insulators.

cond-mat.mes-hall↗

arXiv2014

Absence of the polar Kerr effect in the helical loop-current model [Phys. Rev. Lett. 111, 047005 (2013)]

We correct our claim made in Phys. Rev. Lett. 111, 047005 (2013) that the chiral texture of loop currents can explain the experimentally observed polar Kerr effect in cuprates. Although our model does contain a bulk gyrotropic term and produces a non-zero Faraday effect on transmission, the reflection matrix of light is, nevertheless, symmetric and gives zero polar Kerr effect.

cond-mat.str-el↗

arXiv2013

Proposed Chiral Texture of the Magnetic Moments of Unit-Cell Loop Currents in the Pseudogap Phase of Cuprate Superconductors

We propose a novel chiral order parameter to explain the unusual polar Kerr effect in underdoped cuprates. It is based on the loop-current model by Varma, which is characterized by the in-plane anapole moment N and exhibits the magnetoelectric effect. We propose a helical structure where the vector N^(n) in the layer n is twisted by the angle pi/2 relative to N^(n-1), thus breaking inversion symmetry. We show that coupling between magnetoelectric terms in the neighboring layers for this structure produces optical gyrotropy, which results in circular dichroism and the polar Kerr effect.

cond-mat.supr-con↗