arXiv subjects

Konstantin S. Denisov

Publications and source records attributed to Konstantin S. Denisov.

7 recordsLinked to original sources

arXiv2026

Magnon Polarization Textures and Transport in Antiferromagnets and Altermagnets

Antiferromagnets (AFMs) host magnons that can exhibit fully circular, elliptic and linear polarizations of sublattice magnetization dynamics. We analyze theoretically different momentum-space magnon polarization textures and magnon transport in collinear AFMs and altermagnets (AMs). The sensitivity of the polarization texture to a magnon momentum direction determines two regimes of magnon polarization kinetics: The Dyakonov-Perel relaxation or its dephasing due to asynchronous Larmor precession. For an easy-axis AFM, magnetic field parallel to the N{é}el vector leads to the suppression of the magnetic dipolar interaction-induced Dyakonov-Perel relaxation, accompanied by the increase in the magnon spin-diffusion length and its counter-intuitive growth with temperature. For a perpendicular orientation, instead, relaxation of circular polarization of magnons is enhanced due to Larmor precession. Finally, extremely anisotropic relaxation of magnon polarization is predicted for AMs or AFMs having Dzyaloshinskii-Morya interaction.

cond-mat.other↗

arXiv2026

Valleytronics in 2D Materials Roadmap

Valleytronics exploits non-equivalent energy extrema in the electronic band structure of crystalline solids -- the valley degree of freedom -- to encode, manipulate, and read out information. The advent of 2D materials, first graphene and then transition-metal dichalcogenides, made valley control practical through optical, electrical, and magnetic routes. This foundation has enabled remarkable progress in recent years spanning established frontiers, such as valley exciton physics and valley Hall effects, as well as emerging directions including lightwave valleytronics, nanophotonic integration, flat-band valleytronics, and spin-valley qubits. In parallel, there are sustained efforts to scale up valleytronic materials and to predict new valleytronic platforms. This Roadmap brings together perspectives from leading experts to chart the key opportunities and challenges at the forefront of 2D material valleytronics. Each section captures a snapshot of progress in a key research area, identifies critical open challenges, and outlines pathways toward future valleytronics breakthroughs.

cond-mat.mes-hall↗

arXiv2025

Symmetry Classification for Alternating Excitons in Two-Dimensional Altermagnets

Excitons, bound electron-holes states, often dominate the optical response of two-dimensional (2D) materials and reflect their inherent properties, including spin-orbit coupling, magnetic ordering, or band topology. By focusing on a growing class of collinear antiferromagnets with a nonrelativistic spin splitting, referred to also as altermagnets (AM), we propose a theoretical framework based on the spin space group (SSG) to elucidate their resulting excitons. Our approach is illustrated on 2D AM with spin-polarized valleys, where we classify the combination of conduction and valence bands by the SSG representations into two cases that hosts bright $s$-like and $p$-like excitons, respectively. This analysis is further supported by effective Hamiltonians and the Bethe-Salpeter equation. We identify the excitonic optical selection rules from the calculated absorption spectra and the symmetry of bright excitons from their momentum space envelope functions. Our framework provides optical fingerprints for various cases of AM, while their tunability, such as the strain-induced valley splitting, is also transferred to excitons allowing, additionally, valley-polarized photocurrent generation.

cond-mat.mes-hall↗

arXiv2025

Tunable resonant s-p mixing of excitons in van der Waals heterostructures

Excitonic states of tightly-bound electron-hole pairs dominate the optical response in a growing class of two-dimensional (2D) materials and their van der Waals (vdW) heterostructures. In transition metal dichalcogenides (TMDs) a useful guidance for the excitonic spectrum is the analogy with the states in the 2D hydrogen atom. From our symmetry analysis and solving the Bethe-Salpeter equations we find a much richer picture for excitons and predict their tunable resonant s-p mixing. The resonance is attained when the subband splitting matches the energy difference between the 1s and 2p+ (or 2p-) excitons, resulting in the anticrossing of the spectral lines in the absorption as a function of the subband splitting. By focusing on TMDs modified by magnetic proximity, and gated 3R-stacked bilayer TMD, we corroborate the feasibility of such tunable spin splitting. The resulting tunable and bright s-p excitons provide unexplored opportunities for their manipulation and enable optical detection of Rashba or interlayer coupling in vdW heterostructures.

cond-mat.mes-hall↗

arXiv2025

Movable Dirac Points with Ferroelectrics: Kink States and Berry Curvature Dipoles

Two-dimensional (2D) Dirac states and Dirac points with linear dispersion are the hallmark of graphene, topological insulators, semimetals, and superconductors. Lowering a symmetry by the ferroelectric polarization opens the gap in Dirac points and introduces finite Berry curvature. Combining this with Dirac points detached from high symmetry points of the Brillouin zone offers additional ways to tailor topological properties. We explore this concept by studying topological phenomena emerging in 2D materials with movable Dirac points and broken out-of-plane mirror reflection. The resulting topological kink states and Berry curvature dipoles are changed by movable 2D Dirac points with experimental signatures in electrical conductance and second-harmonic nonlinear Hall conductivity. We identify materials platforms where our predictions can be realized and support that with the first-principles results for Cl$_2$Rh$_2$S$_2$-GeS junction.

cond-mat.mes-hall↗

arXiv2024

Terahertz Spin-Light Coupling in Proximitized Dirac Materials

The two-dimensional (2D) materials are highly susceptible to the influence of their neighbors, thereby enabling the design by proximity phenomena. We reveal a remarkable terahertz (THz) spin-light interaction in 2D Dirac materials that arises from magnetic and spin-orbital proximity effects. The dynamical realization of the spin-charge conversion, the electric dipole spin resonance (EDSR), of Dirac electrons displays distinctive THz features, upon emerging spin-pseudospin proximity terms in the Hamiltonian. To capture the effect of fast pseudospin dynamics on the electron spin, we develop a mean-field theory and complement it with a quantum-mechanical treatment. As a specific example, we investigate the THz response of a single graphene layer proximitized by a magnetic substrate. Our analysis demonstrates a strong enhancement and anomalous polarization structure of the THz-light absorption which can enable THz detection and efficient generation and control of spins in spin-based quantum devices. The identified coupled spin-pseudospin dynamics is not limited to EDSR and may influence a broad range of optical, transport, and ultrafast phenomena.

cond-mat.mes-hall↗

arXiv2024

Anisotropic spin dynamics in antiferromagnets with a nonrelativistic spin splitting

Antiferromagnets (AFM) with a nonrelativistic spin splitting (NSS) of electronic bands expand the range of spin-dependent phenomena and their applications. A crucial understanding for both of them pertains to the inherent spin dynamics. We demonstrate that the $d$-wave NSS gives rise to extremely anisotropic spin dynamics of carriers driven by the relaxation induced by motional narrowing. In contrast to the no relaxation of the spin polarization along the Neel vector, the dynamics of perpendicular spin components greatly varies from a long relaxation for a weak NSS to the fast-decaying oscillations for a strong NSS, a regime relevant to AFM with the $d$-wave NSS. The extreme anisotropy of the spin relaxation is transformed by the external magnetic field, which triggers the relaxation of the parallel spin component and also suppresses all the relaxation rates at larger magnitudes. The predicted spin dynamics of the $d$-wave NSS, known also from altermagnets, can be used as their experimental fingerprints and guide future applications.

cond-mat.mes-hall↗