Speaker
Description
The density matrix is a fundamental quantity of nonequilibrium quantum statistical mechanics, introduced in 1927 shortly after the birth of quantum physics by von Neumann and Landau, which allows us to compute observable quantities in spintronics like spin torque, spin densities, spin currents etc. However, debates have been raging in recent spintronic literature on how to construct density matrix properly in linear-response stead-state nonequilibrium via Kubo or Keldysh formulas, as their recent usage has produced apparently vastly different physical conclusions. For time-dependent systems, such as 2D antiferromagnet CrSBr driven by femtosecond laser pulses, one further needs to properly construct a time-dependent density matrix and include excitons within it to explain very recent experiments on optical excitation of magnons via exciton mediation. This talk will explain recently achieved full resolution [1] of “debates raging in the literature” via examples of spin-orbit torque [2] in proximitized graphene, computed via both Kubo and Keldysh formulas for the density matrix with proper inclusion of dissipation effects; as well as explain [3] how magnons, of finite life-time due to dissipation, are optically excited in CrSBr and how they can be detected via new signatures in pumped current or emitted electromagnetic radiation.
[1] S. M. João, M. D. Petrović, J. M. Viana Parente Lopes, A. Ferreira, and B. K. Nikolić, arXiv:2408.16611 (2024).
[2] K. Dolui, M. D. Petrović, K. Zollner, P. Plecháč, J. Fabian, and B. K. Nikolić, Nano Lett. 20, 2288 (2020).
[3] J. Varela-Manjarres, Y. Ren, and B. K. Nikolić, in preparation.
