arXiv subjects

S. S. Apostoloff

Publications and source records attributed to S. S. Apostoloff.

6 recordsLinked to original sources

arXiv2026

Manipulation of magnetic skyrmions by non-uniform electric fields

Magnetic skyrmions are topologically protected spin textures in ferromagnetic materials that hold great promise for both classical information storage and processing, as well as for fault-tolerant quantum computing. Realizing practical skyrmion-based devices demands an energy-efficient and precise method for their flexible manipulation. In this paper, we theoretically propose such a tool, leveraging the magnetoelectric effect induced by a localized electric field generated by one or several charged tips. Combining complementary numerical simulations and analytical approaches, we develop a consistent theory describing the stability and dynamics of Néel-type skyrmions under the influence of the electric field from a charged tip. Specifically, we demonstrate that the electric field can create, drive, and annihilate skyrmions of both chiralities, as well as more complex textures such as skyrmioniums and target skyrmions. We identify several distinct dynamical regimes of skyrmion motion near the tip and map them onto a phase diagram. Finally, we discuss the feasibility of a practical device capable of controlled skyrmion manipulation based on this principle.

cond-mat.mes-hall↗

arXiv2026

Majorana bound states in chiral ferromagnet-superconductor heterostructures revisited

Majorana zero modes are central to the pursuit of fault-tolerant topological quantum computation. While traditionally sought in one-dimensional hybrid nanowires, a robust alternative platform involves heterostructures combining superconductors with noncollinear magnets. This work focuses on a particularly promising system: a chiral ferromagnet hosting a magnetic skyrmion coupled to a superconducting film containing a superconducting vortex. Such skyrmion-vortex pairs have recently been realized experimentally and are theorized to harbor localized Majorana states, offering a potential pathway for braiding operations. We present a comprehensive theoretical analysis of the low-energy quasiparticle bound states in these heterostructures. Extending previous studies, we develop an analytical framework for the Majorana wavefunctions as well as the wavefunctions and spectrum of other lowlying states within a Bogoliubov-de Gennes approach. Our analytical results explicitly demonstrate the critical role of spin-orbit coupling for the stabilization of Majorana modes and provides approximate analytical expressions for low-lying states localized at the vortex, both with and without an accompanying skyrmion. The derived analytical results show excellent agreement with numerical simulations. We further elucidate the role of realistic effects, including vector potentials and texture perturbations from stray magnetic fields, to assess their impact.

cond-mat.mes-hall↗

arXiv2025

The Effect of Pearl Vortices on the Shape and Position of Néel-Type Skyrmions in Superconductor-Chiral Ferromagnet Heterostructures

This review presents recent work carried out at the Landau Institute for Theoretical Physics of the Russian Academy of Sciences on the study of the effect of superconducting vortices on the shape and position of Néel-type skyrmions in superconductor--chiral ferromagnet heterostructures. Based on analytical and numerical approaches, a number of effects caused by the inhomogeneous magnetic field of the vortex have been predicted: a significant increase in the skyrmion radius, a change in its chirality in the case of a coaxial configuration of the vortex and skyrmion, and modification of the skyrmion shape in the case of an eccentric configuration. Recent experiments studying these effects are discussed.

cond-mat.supr-con↗

arXiv2024

Bound states and scattering of magnons on a superconducting vortex in ferromagnet-superconductor heterostructures

We study the magnon spectrum in a thin ferromagnetic-superconductor heterostructure in the presence of a single superconducting vortex. We employ the Bogolubov-de Gennes Hamiltonian which describes the magnons in the presence of the stray magnetic field and the non-uniform magnetic texture induced by the vortex. We find that the vortex localizes magnon states approximately in the same way as a charge center produces electron bound states due to screened Coulomb interaction in the two-dimensional electron gas. The number of these localized states is substantially determined by the material parameters of the ferromagnetic film only. We solve the scattering problem for an incident plane spin wave and compute the total and transport cross sections. We demonstrate that the vortex-induced non-uniform magnetic texture in chiral ferromagnetic film produces a skew scattering of magnons. We explore the peculiarities of the quantum scattering problem that correspond to orbiting in the classical limit.

cond-mat.mes-hall↗

arXiv2024

Deformation of a Néel-type Skyrmion in a Weak Inhomogeneous Magnetic Field: Magnetization Ansatz and Interaction with a Pearl Vortex

In this work, we develop a theory of (meta)stable states of Néel-type skyrmions in weak nonuniform magnetic fields. We claim an Ansatz for modeling the non-symmetric magnetization that can be implied for both analytics and numerical simulations. Our theory accounts for changes in the size of skyrmion parameters and also includes deformations from the centrally symmetric shape. The ansatz streamlines the analytic calculation of the skyrmion free energy, enhancing the efficiency of the minimizing process. Performing the minimization in two stages, one can find all the minima, global and local, of the free energy, discovering the stable and metastable states. We apply the developed methodology to investigate the (meta)stable configurations of skyrmions influenced by the stray field of a Pearl vortex. Our study reveals the dependence of skyrmion spatial parameters on the vortex field effective strength and presents a phase diagram identifying regions where metastable configurations are predicted. Corroborated by micromagnetic simulations, our findings offer a detailed perspective on the interaction between magnetic skyrmions and superconducting vortices.

cond-mat.mes-hall↗

arXiv2022

Chirality inversion and radius blow-up of a Néel-type skyrmion by a Pearl vortex

We develop a theory for the coaxial configuration of a Néel-type skyrmion and a Pearl vortex in thin superconductor-chiral ferromagnetic heterostructures. Using direct numerical solution of the Euler-Lagrange equation and micromagnetic simulations we demonstrate that the inhomogeneous magnetic field of the Pearl vortex significantly modifies the skyrmion profile with respect to the one in the absence of the vortex. We discover drastic enlargement of the skyrmion's radius and inversion of the skyrmion's chirality. To unravel physics behind these effects we invent novel two-parameter ansatz for the magnetization profile of the skyrmion in the presence of the vortex. Chirality inversion and radius blow-up are controlled not only by the material parameters of the heterostructure but also by the thickness of the superconductor. Our findings can have implications for Majorana modes localized at skyrmion-vortex pairs.

cond-mat.mes-hall↗