arXiv subjects

Alexander Mitrofanov

Publications and source records attributed to Alexander Mitrofanov.

7 recordsLinked to original sources

arXiv2023

Effects of spin-orbit interaction and electron correlations in strontium titanate

We show that the Bloch states in the conduction band of SrTiO$_3$ arise from the interplay between highly anisotropic hopping in sub-bands derived from the Ti $t_{2g}$ orbitals and spin-orbit coupling that mixes these orbitals. Because of the nearly flat-band characteristics for one of the principal axes, at sufficiently high doping these Bloch states become unstable with respect to electron interactions, resulting in Mott-like singlet correlations. These findings may be relevant to the anomalous electronic properties of SrTiO$_3$, including its unusual superconductivity.

cond-mat.supr-con↗

arXiv2022

Orbital entanglement mechanism of superconductivity in cuprates

We utilize a 1d Hubbard model to show that the superconductivity in cuprate superconductors likely arises due to the orbital entanglement between holes in the copper oxide plane mediated by orbitally-selective charge hopping. The main role of doping required to achieve superconductivity in cuprates is to suppress the Mott correlations and orbital ordering. The proposed mechanism explains superconductivity in other unconventional superconductors, and provides guidance in the search for new high-temperature superconductors.

cond-mat.str-el↗

arXiv2021

Exchange bias without directional anisotropy in Permalloy/CoO bilayers

We utilize transverse ac susceptibility measurements to characterize magnetic anisotropy in archetypal exchange-bias bilayers of ferromagnet Permalloy (Py) and antiferromagnet CoO. Unidirectional anisotropy is observed for thin Py, but becomes negligible at larger Py thicknesses, even though the directional asymmetry of the magnetic hysteresis loop remains significant. Additional magnetoelectronic measurements, magneto-optical imaging, as well as micromagnetic simulations show that these surprising behaviors are likely associated with asymmetry of spin flop distribution created in CoO during Py magnetization reversal, which facilitates the rotation of the latter back into its field-cooled direction. Our findings suggest new possibilities for efficient realization of multistable nanomagnetic systems for neuromorphic applications.

cond-mat.mtrl-sci↗

arXiv2021

Effects of the dynamical magnetization state on spin transfer

We utilize simulations of electron scattering by a chain of dynamical quantum spins, to analyze the interplay between the spin transfer effect and the magnetization dynamics. We show that the complex interactions between the spin-polarized electrons and the dynamical states of the local spins can be decomposed into separate processes involving electron reflection and transmission, as well as absorption and emission of magnons - the quanta of magnetization dynamics. Analysis shows that these processes are substantially constrained by the energy and momentum conversation laws, resulting in a significant dependence of spin transfer on the electron's energy and the dynamical state of the local spins. Our results suggest that exquisite control of spin transfer efficiency and of the resulting dynamical magnetization states may be achievable by tailoring the spectral characteristics of the conduction electrons and of the magnetic systems.

cond-mat.mtrl-sci↗

arXiv2020

Non-classical spin transfer effects in an antiferromagnet

We simulate scattering of electrons by a chain of antiferromagnetically coupled quantum Heisenberg spins, to analyze spin-transfer effects not described by the classical models of magnetism. Our simulations demonstrate efficient excitation of dynamical states that would be forbidden by the semiclassical symmetries, such as generation of multiple magnetic excitation quanta by a single electron. Furthermore, quantum interference of spin wavefunctions enables generation of magnetization dynamics with amplitudes exceeding the transferred magnetic moment. The efficiency of excitation is almost independent of the electron spin polarization, and is governed mainly by the transfer of energy. Non-classical spin transfer may thus enable efficient electronic control of antiferromagnets not limited by the classical constraints.

cond-mat.mtrl-sci↗

arXiv2020

Energy and momentum conservation in spin transfer

We utilize simulations of spin-polarized electron scattering by a chain of localized quantum spins to show that energy and linear momentum conservation laws impose strong constraints on the properties of magnetic excitations induced by spin transfer. In turn, electron's orbital and spin dynamics depends on the dynamical characteristics of the local spins. Our results suggest the possibility to achieve precise control of spin transfer-driven magnetization dynamics by tailoring the spectral characteristics of the magnetic systems and the driving electrons.

cond-mat.mes-hall↗

arXiv2018

Filamentation of Mid-IR pulses in ambient air in the vicinity of molecular resonances

Properties of filaments ignited by multi-millijoule, 90-fs mid-IR pulses centered at 3.9 μm are examined experimentally by monitoring plasma density and losses as well as spectral dynamics and beam profile evolution at different focusing strengths. By softening the focusing from strong (f=0.25 m) to loose (f=7 m) we observe a shift from plasma assisted filamentation to filaments with low plasma density. In the latter case, filamentation manifests itself by beam self-symmetrization and spatial self-channeling. Spectral dynamics in the case of loose focusing is dominated by the non-linear Raman frequency downshift, which leads to the overlap with the CO2 resonance in the vicinity of 4.2 μm. The dynamic CO2 absorption in the case of 3.9-μm filaments with their low plasma content is the main mechanism of energy losses and either alone or together with other nonlinear processes contributes to the arrest of intensity.

physics.optics↗