Vitalii K. Dugaev

The Floquet formalism, developed for systems driven periodically in time, is applied to graphene, including the Rashba spin–orbit and Zeeman terms. Employing the high-frequency approximation, we studied Floquet-induced reconstruction of the Dirac spectrum, Poincaré recurrences, and the associated single-particle recurrences, as well as Lissajous curves. We observed single-particle Floquet subharmonic resonances, closed stroboscopic trajectories, and a Floquet-induced topological Lifshitz-like reconstruction of the low-energy spectrum, including anisotropic Dirac-cone deformation and Dirac-cone merging. Our main focus is on periodic time-driving via femtosecond half-cycle laser pulses. We also analyze the quantum metric—the distance between the initial and evolved wave functions—in terms of the participation rates of different bands and commensurate (non-commensurate) properties of the Floquet eigenvalues. In the weak-driving regime, we observe open curves, indicating non-periodic dynamics in the system. Within the considered single-particle Floquet framework, we identify conditions under which the stroboscopic dynamics is dominated by commensurate Floquet phases, leading to quantum Poincaré recurrences, closed Lissajous trajectories, and subharmonic spin oscillations. These effects are interpreted as Floquet time-crystal-like precursors in the sense of single-particle subharmonic dynamics. Within the presented single-particle Floquet framework, Poincaré recurrences and Lissajous resonances provide criteria for closed stroboscopic trajectories and subharmonic Floquet resonances.

A magnetic field typically suppresses superconductivity by either breaking Cooper pairs via the Zeeman effect or inducing vortex formation. However, under certain circumstances, a magnetic field can stabilize superconductivity instead. This seemingly counterintuitive phenomenon is associated with magnetic interactions and has been extensively studied in three-dimensional materials. By contrast, this phenomenon, hinting at unconventional superconductivity, remains largely unexplored in two-dimensional systems, with moiré-patterned graphene being the only known example. Here, we report the observation of reentrant superconductivity at the epitaxial (110)-oriented LaTiO ₃ -KTaO ₃ interface. This phenomenon occurs across a wide range of charge carrier densities, which, unlike in three-dimensional materials, can be tuned in situ via electrostatic gating. We propose that the observed reentrant superconductivity can arise from an interplay between strong spin-orbit coupling and a magnetic field–driven modification of the Fermi surface. Our findings provide insight into reentrant superconductivity and establish a robust platform for exploring unconventional superconducting phenomena in two-dimensional systems.

Altermagnetism became very popular because of unique features, namely coupling between magnetic properties and momentum of itinerant electrons. The particular model of the altermagnetic system of our interest has already been studied in recent publications in a different context: . Here, we study the scattering process of an itinerant electron from the altermagnetic material on the electron localized in a GaAs quantum dot doped on the altermagnetic material. We found a spatially inhomogeneous distribution of quantum entanglement in the postscattering state. An interesting observation is the spatially anisotropic distribution of concurrence which depends on the values of the altermagnetic spin-orbit interaction constant. We also studied Rényi entropy and the effect of disorder in the system leading to randomness in the spin-orbit constant. Our main finding is that, due to the unique properties of an altermagnetic system, tuning the applied external magnetic field allows tailoring of the desired entangled state. Thus the scattering process, in essence, mimics the Hadamard-CNOT gate transformation, converting the initial disentangled state into the entangled state of Bell's state. In particular, we achieved more than 70 % fidelity between the postscattering and Bell's states. Published by the American Physical Society 2025

We study the superconducting Josephson junction diode operating via the magnetic field of skyrmions. Inspired by the near-field optical microscopy, we propose to partially screen the magnetic field and analyze part by part the magnetic texture of the skyrmion. The detected asymmetric supercurrent is influenced by the skyrmionic magnetic field and magnetic texture. This enables the Josephson junction diode to function as a hyperfine sensor and to read out the information about the morphology of the complex magnetic textures. The proposed setup opens another avenue in magnetometry and represents an alternative to the technologies based on the nitrogen-vacancy centers.

Simultaneous manipulation of charge and spin density distributions in materials is the key element required in spintronics applications. Here we study the formation of coupled spin and charge densities arising in scattering of electrons by domains of local magnetization producing a position-dependent Zeeman field in the presence of the spin-momentum locking typical for topological insulators. Analytically and numerically calculated scattering pattern is determined by the electron energy, domain magnetization, and size. The spin-momentum locking produces strong differences with respect to the spin-diagonal scattering and leads to the scattering asymmetry with a nonzero mean scattering angle as determined by only two parameters characterizing the system. To extend the variety of possible patterns, we study scattering by diffraction gratings and propose to design them in modern nanostructures based on topological insulators to produce desired distributions of the charge and spin densities. These results can be useful for engineering of magnetic patterns for electron optics to control coupled charge and spin evolution.