arXiv subjects

Sergey Artyukhin

Publications and source records attributed to Sergey Artyukhin.

At least 19 recordsLinked to original sources

arXiv2026

Exchange striction determines how fast antiferromagnetic insulators demagnetize

Antiferromagnets combine terahertz spin dynamics with insensitivity to stray fields, and how quickly their order can be manipulated sets the speed limit on device operation. Femtosecond optical pulses demagnetize antiferromagnetic insulators on timescales that span picoseconds to nanoseconds across compounds, and no material parameter is known that accounts for the spread or predicts where a new compound will fall. In a compensated antiferromagnet, no angular momentum needs to leave the spin system, so the rate is set by energy flow from the lattice into the spins. Time-resolved second-harmonic generation experiments show that Cr2O3 demagnetizes within 2 ps once the lattice is driven above the Neel temperature, two orders of magnitude faster than the structurally similar FeBO3. First-principles calculations trace the disparity to exchange striction: short Cr-Cr contacts make the exchange coupling tenfold more sensitive to atomic displacements and widen the phase space for phonon decay into magnon pairs. Spin-lattice simulations with ab initio parameters reproduce the order of magnitude of the measured ratio. The derivative of the exchange coupling with respect to the ionic displacement thus emerges as a computable parameter that predicts how fast an insulating antiferromagnet can be demagnetized. The results advance our understanding of ultrafast control in insulating antiferromagnets, and suggest a practical pathway to screen candidate materials for thermally assisted antiferromagnetic memory before synthesis.

cond-mat.mtrl-sci↗

arXiv2026

Phase-Space Quantum Geometry Beyond Adiabatic Electron Dynamics

The geometry of electronic quantum states plays an important role in the equilibrium and transport properties of solids. While the Berry curvature is known to influence electron motion, recent work has shown that the quantum metric also affects the motion of electron wave packets beyond the adiabatic approximation. To connect this nonadiabatic dynamics to many-electron observables, we derive an equivalent semiclassical formulation, valid up to second order in $\hbar$. The resulting phase-space measure and kinetic equation incorporate the quantum metric over the full phase space, including its mixed real-momentum components. We show that, in spatially inhomogeneous systems, the full phase-space quantum metric contributes to electric polarization in insulators and generates an intrinsic linear Hall response in metals. As a concrete example, we study Dirac electrons subject to a magnetic texture and a background potential that vary periodically in space. In this model, the mixed components of the phase-space metric produce a Hall contribution controlled by the relative phase between the two modulations. This phase-sensitive response can remain finite even when the conventional anomalous Hall conductivity vanishes. More broadly, our formulation enables the systematic study of equilibrium and transport responses in systems whose quantum geometry involves both position and momentum.

cond-mat.mes-hall↗

arXiv2026

Topological pumping of bimerons in spiral magnets

Precise positioning of topological defects is essential for racetrack memories, where their positions along a magnetic nanotrack encode information. Traditional methods achieve nanometric precision by engineering pinning landscapes that enforce discrete steps in defect motion. However, accessing each bit requires overcoming a depinning threshold, which increases power consumption. Here, we demonstrate that spiral magnets provide a natural ruler, enabling precise positioning of bimerons (topological spin textures analogous to skyrmions) without relying on engineered pinning sites. A rotating magnetic field couples directly to the bimeron position, displacing it by exactly one spiral period per full rotation of the field. Such quantized transport of skyrmionic textures, reminiscent of Thouless pumping, is topologically protected and remains robust against perturbations, positioning spiral magnets as a natural skyrmion racetrack. The findings establish a paradigm for topologically protected transport of spin textures.

cond-mat.str-el↗

arXiv2026

Thermal conductivity in noncollinear magnets

Magnetic memory and logic devices, including prospective ones based on skyrmions, inevitably produce heat. Thus, controlling heat flow is essential for their performance. Here we study how non-collinear spin arrangement affects the magnon contribution to thermal conductivity. As a paradigm system, we consider the most basic non-collinear magnet with a spin spiral ground state. Spin noncollinearity leads to anharmonic terms, resulting in magnon fusion and decay processes. These processes determine the magnon lifetime, which can be used to estimate thermal conductivity in a single-mode approximation. However, by solving the full Boltzmann equation numerically, we find a much higher thermal conductivity. This signifies that heat is carried not by individual magnons but by their linear combinations -- relaxons. The thermal conductivity is found to increase with the diminishing spiral pitch, consistent with recent experiments. The results provide the blueprint for calculating magnetic thermal transport in non-collinear magnets.

cond-mat.str-el↗

arXiv2026

Phase Transitions in Low-Dimensional Layered Double Perovskites: The Role of the Organic Moieties

Halide double perovskites are an interesting alternative to Pb-containing counterparts as active materials in optoelectronic devices. Low-dimensional double perovskites are fabricated by introducing large organic cations, resulting in organic/inorganic architectures with one or more inorganic octahedral layers separated by organic cations. Here, we synthesize layered double perovskites based on 3D Cs2AgBiBr6 that consist of double (2L) or single (1L) inorganic octahedral layers, using ammonium cations of different size and chemical structure. Temperature-dependent Raman spectroscopy reveals phase transition signatures in both inorganic lattice and organic moieties by detecting variations in their vibrational modes. Changes in the conformational arrangement of the organic cations to an ordered state coincide with a phase transition in the 1L systems with the shortest ammonium moieties. Significant changes of photoluminescence intensity observed around the transition temperature suggest that optical properties may be deeply affected by the octahedral tilts emerging at the phase transition.

cond-mat.mtrl-sci↗

arXiv2025

Observation of relativistic domain wall motion in amorphous ferrimagnets

Domain walls in ferrimagnets and antiferromagnets behave as relativistic sine-Gordon solitons with the spin-wave group velocity setting the ultimate velocity of domain walls and speed of magnetic devices. While this relativistic regime has been achieved in crystalline ferrimagnets, they cannot be routinely integrated in devices. To enable technological breakthroughs, relativistic dynamics must be demonstrated in easy-to-integrate ferrimagnets such as rare-earth -- transition-metal alloys. However, this scenario remains elusive due to the inherent magnetic disorder of these materials, complex spin-wave spectra, and challenges in modeling their ultrafast dynamics. Here, we demonstrate relativistic domain wall motion in amorphous ferrimagnetic GdFeCo devices operated in the proximity of the angular momentum compensation point. The current-induced domain wall velocity saturates within 10% of the spin-wave speed of 2 km/s, a behavior consistent with relativistic model of domain wall motion. Our observation of relativistic dynamics in technologically relevant ferrimagnets opens the way to magnetic devices operating at the ultimate speed limit.

cond-mat.mtrl-sci↗

arXiv2025

Finite temperature magnetic interactions from first principles

Density functional theory has demonstrated remarkable predictive power in calculating magnetic properties at zero temperature. At finite temperatures, thermally excited phonons may affect magnetism. Efficient ab-initio methods to calculate the temperature dependence of magnetic exchange interactions are still lacking despite the importance of room temperature magnetism for applications. Exchange is controlled by an interplay between metal-ligand hybridization, Hubbard repulsion, band gap, interatomic distances and bond angles, all of which change with temperature. Here we present a method to calculate the exchange interactions at finite temperatures from first principles using only two supercell calculations and quantify these mechanisms. Changes in bond angles and the band gap are identified as a primary factors. In NiO with 180-degree bonds exchange decreases with temperature, while in Cr$_2$O$_3$ with the bond angles away from 180 degrees the exchange increases by 10% at room temperature.

cond-mat.str-el↗

arXiv2025

Merons, hedgehogs and magnetoelectric switching in spiral multiferroics

In spiral multiferroics, magnetism induces ferroelectricity, thus holding a promise for novel memory devices where an electric field switches magnetic bits. However, such a switching process, in which magnetic domain walls are moved electrically, is still poorly understood. We find multiferroic domain walls containing arrays of meron (half-skyrmion) strings with a plethora of topological defects, which profoundly affect wall dynamics. Minimum energy walls have alternating meron topological charges and move as relativistic massive particles, with velocity limited by the magnon speed. During domain nucleation, walls with non-alternating meron charges appear. Such defects result in a peculiar non-local dynamics where all the spins in the system rotate, and the wall mobility is suppressed. Meron strings possess 0D hedgehog defects, analogous to Bloch points, that pin the wall to the lattice. This fascinating interplay of magnetoelectric switching with a variety of topological defects and non-local spin dynamics opens a new playground for the electric manipulation of spins.

cond-mat.str-el↗

arXiv2024

Entangled orbital, spin, and ferroelectric orders in $p$-electron magnet CsO$_2$

Alkali superoxides differ from conventional transition metal magnets, exhibit magnetism from partially occupied oxygen molecular $π^*$-orbitals. Among them, CsO$_2$ stands out for its potential to exhibit novel quantum collective phenomena, such as an orbital order induced Tomonaga-Luttinger liquid state. Using ab-initio Hubbard models, superexchange theory, and experimental spin wave measurements, we propose that CsO$_2$ exhibits unconventional magnetoelectric characteristics at low temperature. Our analysis confirms a canted antiferromagnetic ground state and a spin-flop transition, with ferroelectricity is induced by breaking inversion and time-reversal symmetry in the spin-flop phase. Consequently, our analysis reveals a strong interplay not only between exchange interactions but also among magnetically-induced polarization and orbital order. The magnetic structure, stabilized by orbital order, induces magnetically-induced polarization through an antisymmetric mechanism. Overall, our results reveal the coexistence of three highly entangled orders in CsO$_2$, namely, orbital, spin and ferroelectricity.

cond-mat.str-el↗

arXiv2024

Multiferroic kinks and spin-flop transition in Ni$_{2}$InSbO$_6$ from first principles

Magnetoelectric multiferroics are key materials for next-generation spintronic devices due to their entangled magnetic and ferroelectric properties. Spiral multiferroics possess ferroelectric polarization and are particularly promising for electric control of magnetism and magnetic control of ferroelectricity. In this work, we uncover long-period incommensurate states characterized by unique multiferroic kinks in corundum nickelate Ni$_{2}$InSbO$_6$, a member of a promising family of polar magnets. Utilizing a 2-orbital $S=1$ model, we derive formulas for Heisenberg and anisotropic magnetic exchanges and magnetically-induced polarization, enabling their calculations from first principles. We use these parameters in Monte Carlo and Landau theory-based calculations to reproduce experimentally observed magnetic structures and polarization dependence on the magnetic field. We predict magnetic phase transitions between flat spiral, conical spiral, canted antiferromagnetic and ferromagnetic states under increasing magnetic fields. Kinks in the spiral phases repel each other through a Yukawa-like potential arising from exchange of massive magnons. We also find that suitably directed electric fields can be used to stabilize the ferromagnetic and spiral states. The findings open a new pathway to predictive first-principles modelling of multiferroics and will inspire experiments and technological applications based on multiferroic kinks.

cond-mat.mtrl-sci↗

arXiv2024

Interplay of trimerization, chirality and ferroelecticity in multiferroic BaCoSiO4

Multiferroic materials combine multiple ferroic orders that may enable cross-functionalities, e.g. control of one ferroic order by the field conjugate to the other one. BaCoSiO$_4$, a recently proposed multiferroic combines multiple unit cell-tripling modes, structural chirality and ferroelectric polarization, whose interactions result in a peculiar ground state. We derive the Landau free energy for interacting trimerization, electric polarization and structural chiral modes and find the corresponding coefficients from first-principles calculations. This results in a quantitative model for the description of domain walls and vortices, observed in recent experiments.

cond-mat.mtrl-sci↗

arXiv2024

Electric field-induced domain wall motion in spin spiral multiferroics

Switching in magnetic materials gives rise to rich physical phenomena and lies at the heart of their technological applications. Although domain wall motion in ferro- and antiferromagnets has been studied, in spiral magnets it is still poorly understood despite 20 years of active research since the discovery of spiral multiferroics. The problem of the domain wall motion in a spiral magnet is a compelling one, the more so the magnetic domain walls in cycloidal spiral phase are also ferroelectric, thus enabling electric control of magnetism, i.e. domain wall motion under the action of an external electric field. Phase transition to a spiral phase leads to a formation of chiral domains with opposite spin rotation senses, that are separated by chiral domain walls. Spiral order breaks inversion symmetry and induces a ferroelectric polarization, whose sign is determined by the chirality of the domain. Thus the spiral order allows for the manipulation of spins via an external electric field. Here we study domain wall motion in magnets with spiral ground state, that are the most basic non-collinear magnets. We formulate a simplified variational model and derive the equation of motion for the domain wall driven by an external electric field. The results are corroborated with atomistic spin dynamics simulations. The results suggest a linear dependence of the wall speed on the external electric field, and a peculiar dependence on the system geometry and domain structure.

cond-mat.str-el↗

arXiv2022

Microscopic Origin of the Electric Dzyaloshinskii-Moriya Interaction

The microscopic origin of the electric Dzyaloshinskii-Moriya interaction (eDMI) is unveiled and discussed by analytical analysis and first-principles based calculations. As similar to the magnetic Dzyaloshinskii-Moriya interaction (mDMI), eDMI also originates from electron-mediated effect and more specifically from certain electron hoppings that are being activated due to certain local inversion symmetry breaking. However, the eDMI energy is found to be at least a third-order interaction in atomic displacements instead of bilinear in magnetic dipole moments for mDMI. Furthermore, the eDMI energy form is presented, and we find that novel electrical topological defects (namely, chiral electric bobbers) can arise from this eDMI. Thus unraveling the microscopic origin of eDMI has the potential to lead to, and explain, the discovery of novel polar topological phases.

cond-mat.mtrl-sci↗

arXiv2022

Ferroelectricity and topological vortices from molecular ordering in metal-organic frameworks

Metal-organic frameworks comprehend a wide class of hybrid organic-inorganic materials with general structure A$_m$BX$_n$, with $A$ and $X$ being organic molecules and B a metal cation. This often results in enhanced structural flexibility and new functionalities. Hybrid perovskites ABX$_3$ are a well-known example.} In an Iron-based perovskites, (DMA)Fe^{II-III}(COOH)_3, dimethylammonium (DMA) molecules are organized in a hexagonal structure. They are orientationally disordered at high temperatures, but order at around $T=100$~K in a peculiar toroidal pattern. Recent experimental and theoretical study suggest the appearance of ferroelectric polarization in this phase, although the measured polarization is small, and the mechanism of ferroelectricity is still debated. We formulate a Landau-type theory that clarifies the connection between the electric polarization, molecular pattern, and distortive modes of the inorganic lattice. We find a remarkable mechanism of improper ferroelectricity, analogue to the trimerization process in inorganic hexagonal ferrites and manganites, but here driven by the ordering of organic molecules in a metal-organic framework. Our study reveals an extremely rich phase diagram with the prediction of topological domain walls, where the ferroelectricity arise from tripling the unit cells due to molecular ordering. Wide domain walls with inner structure are predicted.

cond-mat.mtrl-sci↗

arXiv2020

Soft magnon contributions to dielectric constant in spiral magnets with domain walls

Competing magnetic exchange interactions often result in non-collinear magnetic states, such as spin spirals, which break the inversion symmetry and induce ferroelectric polarization. The resulting strong interactions between magnetic and dielectric degrees of freedom lead to a technologically important possibility to control magnetic order by electric fields and to electromagnons, magnetic excitations that can be excited by an electric dipole of the electromagnetic field. Here we study the effects of chiral domain walls on magnetoelectric properties of spiral magnets. We use a quasi-1D model Hamiltonian with competing Heisenberg exchange interactions, leading to a spin spiral, and Dzyaloshinskii-Moriya interactions, that couple spins and electric dipoles and mix magnon and phonon excitations. The results suggest that low frequency dielectric anomalies in spiral magnets, such as TbMnO3 and MnWO4, may originate from hybrid magnon - polar phonon excitations associated with domain walls.

cond-mat.str-el↗

arXiv2020

A Semi-Classical View on Epsilon-Near-Zero Resonant Tunneling Modes in Metal/Insulator/Metal Nanocavities

Metal/Insulator/Metal nanocavities (MIMs) are highly versatile systems for nanometric light confinement and waveguiding, and their optical properties are mostly interpreted in terms of surface plasmon polaritons. Although classic electromagnetic theory accurately describes their behavior, it often lacks physical insight, letting some fundamental aspects of light interaction with these structures unexplored. In this work, we elaborate a quantum mechanical description of the MIM cavity as a double barrier quantum well. We identify the square of the imaginary part of the refractive index of the metal as the optical potential, and find that MIM cavity resonances are suppressed if the ratio n/\k{appa} exceeds a certain limit, which shows that low n and high \k{appa} are desired for strong and sharp cavity resonances. Interestingly, the spectral regions of cavity mode suppression correspond to the interband transitions of the metals, where the optical processes are intrinsically non-Hermitian. The quantum treatment allows to describe the tunnel effect for photons, and reveals that the MIM cavity resonances can be excited by resonant tunneling via illumination through the metal, without the need of momentum matching techniques such as prisms or grating couplers. By combining this analysis with spectroscopic ellipsometry on experimental MIM structures, and by developing a simple harmonic oscillator model of the MIM for the calculation of its effective permittivity, we show that the cavity eigenmodes coincide with low-loss zeros of the effective permittivity.

physics.app-ph↗

arXiv2020

Liberation of slave modes inside domain walls in multiferroic Cu-Cl boracite

Domain walls (DWs), the two-dimensional boundaries between symmetry equivalent ferroic domains, are actively investigated due to their promise for novel logic and memory devices. Moreover, they can be easily created, erased and reshaped at a low energy cost due to their high mobility and large electrical conductivity. Most work so far has been focused on DWs in proper ferroelectrics, where the primary order parameter, ferroelectric polarization, interpolates between the values in the domains by either reducing to zero (in Ising-type DW) or rotating (Bloch type DW). Here we present a new member of DW family with a complex inner texture of slave order parameters inside the wall where the primary order parameter reduces to zero. Our first-principles-derived model predicts the existence of monopolar and toroidal polarization patterns. The results enable large-scale phase field simulations of complex domain patterns in boracites and could inspire novel devices based on domain walls in improper ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2020

Unexpected Giant Microwave Conductivity in a Nominally Silent BiFeO3 Domain Wall

Nanoelectronic devices based on ferroelectric domain walls (DWs), such as memories, transistors, and rectifiers, have been demonstrated in recent years. Practical high-speed electronics, on the other hand, usually demand operation frequencies in the giga-Hertz (GHz) regime, where the effect of dipolar oscillation is important. In this work, an unexpected giant GHz conductivity on the order of 103 S/m is observed in certain BiFeO3 DWs, which is about 100,000 times greater than the carrier-induced dc conductivity of the same walls. Surprisingly, the nominal configuration of the DWs precludes the ac conduction under an excitation electric field perpendicular to the surface. Theoretical analysis shows that the inclined DWs are stressed asymmetrically near the film surface, whereas the vertical walls in a control sample are not. The resultant imbalanced polarization profile can then couple to the out-of-plane microwave fields and induce power dissipation, which is confirmed by the phase-field modeling. Since the contributions from mobile-carrier conduction and bound-charge oscillation to the ac conductivity are equivalent in a microwave circuit, the research on local structural dynamics may open a new avenue to implement DW nano-devices for RF applications.

cond-mat.mtrl-sci↗