arXiv subjects

S. V. Streltsov

Publications and source records attributed to S. V. Streltsov.

At least 19 recordsLinked to original sources

arXiv2026

Jsymm: A Python package for symmetry analysis of exchange tensors in magnetic Hamiltonians

Symmetries of a crystal often restrict its physical properties. In particular, they determine possible forms of the tensors that describe interatomic exchange interaction, which governs a wide range of magnetic phenomena. Computationally demanding first-principles calculations of the exchange tensors can be greatly simplified by taking the symmetry constraints into account. Here, we present Jsymm, a Python package that derives the most general symmetry-compatible form of the exchange tensors directly from the crystallographic data. For any bond formed by magnetic ions, Jsymm produces the tensors of the Dzyaloshinskii-Moriya and anisotropic Heisenberg exchange interaction in symbolic form, as well as the tensors for all other bonds related to it by symmetry. This reduces the number of independent model parameters, dramatically lowering the computational cost of the ab initio calculations and preventing unphysical results arising from symmetry violations. The package accepts standard CIF files and provides a web interface in addition to an interactive text mode and a Python library. We demonstrate its utility on La$_2$CuO$_4$ and $\alpha$-Fe$_2$O$_3$, reproducing known symmetry constraints and revealing additional relations between components of the exchange tensors of different bonds.

cond-mat.mtrl-sci↗

arXiv2026

Orbital-specific Itinerancy and Localization in a Kagome Magnet

The kagome lattice naturally hosts flat bands, Dirac fermions, and van Hove singularities, yet whether its geometry can stabilize orbital-selective phases - a hallmark of Hund's physics in multi-orbital correlated systems - has remained an open question. Here, we combine resonant inelastic X-ray scattering with density functional theory and dynamical mean-field theory to demonstrate that YMn$_6$Sn$_6$ exhibits a spontaneous orbital differentiation into coexisting itinerant and localized electrons within the same Mn $3d$ manifold. Orbitals directed along Mn-Mn bonds provide coherent quasiparticles and metallic bands, while those pointing toward ligands become strongly correlated and display non-Fermi-liquid behavior. Hund's intra-atomic exchange suppresses orbital fluctuations, stabilizing this dichotomy and providing a natural double-exchange-like mechanism for the observed ferromagnetic bilayer coupling. Our work establishes YMn$_6$Sn$_6$ as a kagome platform where orbital selectivity, flat-band topology, and Hund's metallicity converge - revealing that geometric frustration and correlation-driven orbital differentiation can cooperatively design exotic quantum phases beyond the canonical paradigms of Mott physics or band topology alone.

cond-mat.str-el↗

arXiv2026

Monte Carlo study of the classical antiferromagnetic $J_1$-$J_2$-$J_3$ Heisenberg model on a simple cubic lattice

An extensive Monte Carlo study of the classical Heisenberg model on a simple cubic lattice with antiferromagnetic exchange interactions $J_n$ between the first, second, and third neighbors is performed in a broad region of $J_2 / J_1$, $J_3 / J_1$ ratios, and temperature. The character of the phase transitions is analyzed via the Binder cumulant method. The Neel temperature $T_{\mathrm{N}}$ and the frustration parameter (the ratio $f= |\theta|/T_{\mathrm{N}}$, $\theta$ being the Curie-Weiss temperature) are calculated. A comparison with the Tyablikov approximation is carried out. The strength of the frustration effects is explored. Possible applications to antiferromagnetic perovskites, such as CaMnO$_3$ and HgMnO$_3$, are discussed.

cond-mat.str-el↗

arXiv2025

Non-reciprocal circular dichroism of axial phonons coupled to ferro-rotational order

Circular dichroism (CD) in X-ray absorption, defined as the difference in absorption between opposite circular polarizations, is fundamentally enabled by the breaking of time-reversal symmetry or inversion symmetry. It is therefore sensitive to magnetism, chirality, and their interplay. In contrast, the sample symmetry alone is insufficient to determine whether CD in resonant inelastic X-ray scattering (RIXS) is allowed. Rather, RIXS-CD is governed by both the sample symmetry and the scattering geometry. Here, using RIXS, we identify circularly polarized phonons coupled to ferro-rotational order in MnTiO$_3$, which we refer to as ferro-axial phonons. Their excitations provide a direct demonstration of non-reciprocal RIXS-CD, in which the dichroic response changes upon reversing the propagation direction of the incident X-rays, although the system globally preserves both inversion and time-reversal symmetries. We propose that a condensate of these phonons, manifested as standing waves, underlies the ferro-rotational order in MnTiO$_3$. The observed non-reciprocal CD reflects the interplay among photon helicity, phonon polarization, and ferro-rotational order.

cond-mat.str-el↗

arXiv2025

Altermagnetic boosting of chiral phonons

Chirality characterizes the asymmetry between a structure and its mirror image and underlies a wide range of chiral functionalities. In crystallographically chiral materials, phonons with non-zero linear momentum $\textbf{k}$ can acquire a $k$-induced longitudinal magnetization, giving rise to chiral phonons. Helical spin order, with its proper screw-type configuration, breaks all mirror symmetries and therefore carries magnetic chirality. Such helical spins also generate non-relativistic spin splitting for any quasiparticle excitations propagating along the screw axis. To explore the possible connection between chiral phonons and magnetic chirality, we investigated the crystallographically polar and chiral compound (Mn,Ni)$_3$TeO$_6$, which hosts three distinct states: a paramagnetic state, a helical spin state with magnetic chirality, and a collinear spin state without magnetic chirality. We find an approximately tenfold enhancement of chiral-phonon coupling in the helical spin state along the screw axis, compared with both the paramagnetic and collinear spin states. These results identify a new route to amplify chiral phonons through an altermagnetic effect arising from the broken parity-time symmetry in helical spins. %from non-relativistic spin splitting.

cond-mat.str-el↗

arXiv2025

Altermagnetism in 6H perovskites

The combination of a centrosymmetric crystallographic structure with local structural alternations and collinear antiferromagnetism can lead to broken PT (Parity $\times$ Time-reversal) symmetry, resulting in altermagnets with non-relativistic spin-split bands. The 6H perovskites with composition A$_3$BB'$_2$O$_9$ exhibit unique layered structural alternations and typically adopt an antiferromagnetic ground state. Here, we report the discovery that several 6H perovskites are indeed altermagnets exhibiting non-relativistic spin-split bands. We also explore the possible presence of net magnetization due to spin-orbit coupling in these materials, as well as the manifestation of giant piezomagnetism. Since the single crystals of 6H perovskites can be readily grown and cleavable, our findings provide a new avenue to study the cleaved atomically-flat surfaces of altermagnets with advanced experimental techniques such as spin-resolved scanning tunneling microscopy (STM) or spin-resolved angle-resolved photoemission spectroscopy (ARPES) to explore their spin splitting nature.

cond-mat.mtrl-sci↗

arXiv2025

Beyond Germanides: Anomalous Hall Effect in the Silicide LaMn2Si2

By combining symmetry analysis and direct density functional calculations including the spin-orbit coupling, we demonstrate that anomalous Hall effect can be observed in not only germanides with general formula RMn$_2$Ge$_2$, where $R$ is a rare-earth ion or Y. Our calculations predict a large anomalous Hall conductivity in LaMn$_2$Si$_2$, with a non-zero $\sigma_{xy}^{AH}$ component of $-360~\text{S/cm}$, accompanied by a pronounced magneto-optical response. Remarkably, electron doping of LaMn$_2$Si$_2$ is expected to substantially enhance the Hall conductivity, with values reaching up to -650 S/cm. These results suggest that silicides with general formula RM$_2$Si$_2$ can be an interesting platform for studying anomalous Hall effect.

cond-mat.str-el↗

arXiv2025

Magnetoelastic dynamics of the "spin Jahn-Teller" transition in CoTi$_{2}$O$_{5}$

CoTi$_{2}$O$_{5}$ has the paradox that low temperature static magnetic order is incompatible with the crystal structure owing to a mirror plane that exactly frustrates magnetic interactions. Despite no observable structural distortion with diffraction, CoTi$_{2}$O$_{5}$ does magnetically order below $T_{\rm N}$ $\sim$ 25 K with the breaking of spin ground state degeneracy proposed to be a realization of the spin Jahn-Teller effect in analogy to the celebrated orbital Jahn-Teller transition. We apply neutron and Raman spectroscopy to study the dynamics of this transition in CoTi$_{2}$O$_{5}$. We find anomalous acoustics associated with a symmetry breaking strain that characterizes the spin Jahn-Teller transition. Crucially, the energy of this phonon coincides with the energy scale of the magnetic excitations, and has the same symmetry of an optic mode, observed with Raman spectroscopy, which atypically softens in energy with decreasing temperature. Taken together, we propose that the energetics of the spin Jahn-Teller effect in CoTi$_{2}$O$_{5}$ are related to cooperative magnetoelastic fluctuations as opposed to conventional soft critical dynamics which typically drive large measurable static displacements.

cond-mat.str-el↗

arXiv2025

Highly correlated electronic state in a ferrimagnetic quadruple perovskite CuCu$_3$Fe$_2$Re$_2$O$_{12}$

Recently synthesized quadruple perovskite CuCu$_3$Fe$_2$Re$_2$O$_{12}$ possesses strong ferromagnetism and unusual electron properties, including enhanced electronic specific heat. Application of the first principles electronic structure approaches unambiguously shows importance of the many-body effects in this compound. While CuCu$_3$Fe$_2$Re$_2$O$_{12}$ is half-metallic ferrimagnet in the DFT+U method, in the density functional theory (DFT) combined with the dynamical mean-field theory (DMFT) it appears to be a metal. Strong correlations lead to a renormalization of electronic spectrum and formation of incoherent states close to the Fermi level. Electronic specific heat and magnetic properties obtained in the DFT+DMFT approach are in better agreement with available experimental data than derived by other band structure techniques.

cond-mat.str-el↗

arXiv2024

Spin-orbit-entangled electronic structure of Ba$_2$CaOsO$_6$ studied by O $K$-edge resonant inelastic X-ray scattering

Transition-metal ions with $5d^2$ electronic configuration in a cubic crystal field are prone to have a vanishing dipolar magnetic moment but finite higher-order multipolar moments, and they are expected to exhibit exotic physical properties. Through an investigation using resonant inelastic X-ray spectroscopy (RIXS), Raman spectroscopy, and theoretical ligand-field (LF) multiplet and $ab initio$ calculations, we fully characterized the local electronic structure of Ba$_2$CaOsO$_6$, particularly, the crystal-field symmetry of the 5$d^2$ electrons in this anomalous material. The low-energy multiplet excitations from RIXS at the oxygen $K$ edge and Raman-active phonons both show no splitting. These findings are consistent with the ground state of Os ions dominated by magnetic octupoles. Obtained parameters pave the way for further realistic microscopic studies of this highly unusual class of materials, advancing our understanding of spin-orbit physics in systems with higher-order multipoles.

cond-mat.str-el↗

arXiv2024

Anisotropy of exchange interactions in honeycomb ladder compound ReCl5

The Re5+(5d2) compounds possess large spin-orbital interaction which urges for large anisotropy, non-collinear structures and other phenomena. Here we present ReCl5 composed by separate Re2Cl10 units formed by edge-shared chlorine octahedra. It demonstrates the formation of antiferromagnetically ordered state in two steps at TN1 = 35.5 K and TN2 = 13.2 K seen in dc-, ac-magnetic susceptibility and in specific heat. At 4K it can be transformed to the state with spontaneous magnetic moment by relatively weak magnetic field m0H = 0.5 T via metamagnetic phase transition. Ab initio calculations give anisotropic ferromagnetic exchange interactions J1 and J2 within and between rhenium pairs forming the zig-zag chains along the a-axis. Pairs of zig-zag chains are coupled by ferromagnetic interaction J3 along the c-axis into magnetic honeycomb ladders. The ladders are coupled by significantly weaker interaction J4.

cond-mat.mtrl-sci↗

arXiv2024

Raman spectroscopy of Na$_3$Co$_2$SbO$_6$

Raman spectroscopy together with density functional calculations were used to study lattice dynamics in a layered honeycomb cobaltite Na$_3$Co$_2$SbO$_6$, which can host a field-induced phase related with the Kitaev physics. We show that there develops an additional mode well above Neel temperature (at $\approx 200$K) at 525 cm$^{-1}$, which origin can be related to an electronic excitation to one of $j_{3/2}$ doublets. Moreover, our theoretical calculations demonstrate that the highest frequency intensive mode related to the oxygen vibrations is very sensitive to type of the magnetic order. Thus, we propose to use the softening of this mode as a hallmark of the transition to a fully polarized regime, which is stabilized in Kitaev materials in strong magnetic fields.

cond-mat.str-el↗

arXiv2024

Rattling Phonon Modes in Quadruple Perovskites

Rattling phonon modes are known to be origin of various anomalous physical properties such as superconductivity, suppression of thermal conductivity, enhancement of specific heat etc. By means of DFT+$U$ calculations we directly show presence of the rattling mode in the quadruple perovskites CuCu$_3$V$_4$O$_{12}$ and CuCu$_3$Fe$_2$Re$_2$O$_{12}$ and argue that this can develop in others as well. It is demonstrated that Cu ions at $A$ sites vibrate in the center of the icosahedral oxygen O$_{12}$ cages and the corresponding potential has a complicated form with many local minima.

cond-mat.str-el↗

arXiv2023

Magnetic phase diagram and possible Kitaev-like behavior of honeycomb-lattice antimonate Na3Co2SbO6

Recent theoretical studies have suggested that Kitaev physics and such effects as formation of a mysterious spin-liquid state can be expected not only in RuCl3 and iridates, but also in conventional $3d$ transition metal compounds. Using DC and AC magnetometry, thermodynamic and $^{23}$Na nuclear magnetic resonance measurements (NMR) we studied such a candidate material Na3Co2SbO6. A full phase diagram of Na3Co2SbO6 in a wide range of magnetic fields and temperatures is presented. The results demonstrate transformation of the antiferromagnetic structure under the external magnetic field, gradual development of the saturation phase, as well as evidence of gapped behavior in certain parts of the phase diagram

cond-mat.str-el↗

arXiv2022

Magnetic oxides

In this article we give a general survey of the main properties of magnetic oxides - mostly the oxides of transition metals, but sometime also containing rare earths ions. This is a very rich class of materials, among which there are insulators and metals, systems with insulator-metal transitions, and there are among them even high-temperature superconductors. One of the main features of these compounds, which attract to them special attention and which serve as a basis of many applications, are their rich magnetic properties. In this article we discuss the main physical effects determining their behaviour, and describe in detail especially their magnetic properties, but not only. After shortly discussing the basic structure of isolated magnetic ions, we concentrate on the collective effects depending on the interaction between sites, especially exchange interaction, giving rise to different magnetic properties: different types of magnetic ordering in conventional systems, but also more exotic states such as spin liquid states in frustrated systems. We also cover related phenomena in magnetic oxides, such as magnetoelectric and multiferroic behaviour, and discuss at the end their diverse useful properties serving as a basis of many applications.

cond-mat.str-el↗

arXiv2022

S. Vonsovsky and the dawn of the theory of strongly correlated systems

A survey of scientific and social activity of S. V. Vonsovsky is presented. His fundamental works on the theory of electronic properties and magnetism of transition and rare-earth metals and their compounds are reviewed. The historical development of the many-electron polar (preceding the famous Hubbard model) and $s-d(f)$ exchange (''Vonsovsky-Zener'', ''Kondo lattice'') models is considered.

cond-mat.str-el↗

arXiv2022

Interplay of the Jahn--Teller Effect and Spin-Orbit Coupling: The Case of Trigonal Vibronic Modes

We study an interplay between the orbital degeneracy and spin-orbit coupling giving rise to spin-orbital entangled states. As a specific example, we analyze the interaction of electrons occupying triply degenerate single-ion $t_{2g}$ levels with trigonal vibronic modes (the $t\otimes T$ problem). A more general problem of the electron-lattice interaction involving both tetragonal and trigonal vibrations is also considered. It is shown that the result of such interaction crucially depends on the occupation of $t_{2g}$ levels leading to either the suppression or enhancement of the Jahn-Teller effect by the spin-orbit coupling.

cond-mat.mtrl-sci↗

arXiv2022

Orbital-slective behaviour in cubanite CuFe2S3

Using {\it ab initio} band structure calculations we show that mineral cubanite, CuFe$_2$S$_3$, demonstrates an orbital-selective behavior with some of the electrons occupying molecular orbitals of $x^2-y^2$ symmetry and others localized at atomic orbitals. This is a rare situation for $3d$ transition metal compounds explains experimentally observed absence of charge disproportionation, anomalous Mössbauer data, and ferromagnetic ordering in between nearest neighbor Fe ions.

cond-mat.str-el↗