Spin diffusion in 2DEGs & group theory applied to crystal degeneracies and boundary conditions

26/05/2021 - 17:00 até 19:00
Prof. Gerson J. Ferreira
plataforma ZOOM: https://zoom.us/j/908724552 - Senha de acesso: 215283

In this talk I’ll present my two current research topics. First, from Ref. [1], we’ll discuss in detail the diffusive spin dynamics in traditional semiconductors (e.g., GaAs). Later, I’ll show an overview of other projects regarding group theory applied to build kp and tight-binding models. Particularly, in Ref. [2] we show how a site-permutation symmetry may lead to degeneracies larger than those predicted by the usual space groups in crystals, and, from Ref. [3], we will present a connection between the lattice regularization by a Wilson’s mass and the boundary conditions of Dirac-like Hamiltonians. In the end it all comes together as fundamental research on models for semiconductors and topological insulators, and their spintronic applications.

Through most of the talk we’ll focus on the spin diffusion. Here we will present a model built from the (Boltzmann-like) quantum kinetic equation in the Keldysh formalism and its linearization into a drift-diffusion equation for the spin and charge. For single-subband two dimensinal electron gases (2DEGs), it is well known that a persistent spin helix (PSH) regime arises when the Rasbha and Dresselhaus spin-orbit couplings are balanced, yielding a spin dynamics with very large lifetimes. On the other hand, for two subband 2DEGs, the intersubband coupling kills the PSH, but it still shows large spin lifetimes and anisotropies, as shown by recent experiments from Hernandez (IFUSP), Gusev (IFUSP), and collaborators. Our results show that the intersubband scattering adds a new knob to control the spin lifetime with electric fields, being maximum for symmetric quantum wells due to Matthiessen’s rule, and may reach large spin lifetimes even in the absence of a true persistent regime.


[1] I. R. de Assis, R. Raimondi, G. J. Ferreira, “Spin drift-diffusion for two-subband quantum well”, Phys. Rev. B 103, 165304 (2021)

[2]F. Crasto de Lima, G. J. Ferreira, “High-degeneracy points protected by site-permutation symmetries”, Phys. Rev. B 101, 041107(R) (2020)

[3] A. L. Araújo, R. P. Maciel, R. G. F. Dornelas, D. Varjas, G. J. Ferreira, “Interplay between boundary conditions and Wilson’s mass in Dirac-like Hamiltonians”, Phys. Rev. B 100, 205111 (2019).

Link para seminário online (plataforma ZOOM): https://zoom.us/j/908724552

Senha de acesso: 215283

OBS: Ao clicar no link seu computador (celular, tablet, ipad, etc.) automaticamente instalará o programa. Se não entrar automaticamente clique em join a meeting ou entrar em uma reunião e digite a sequência de 9 dígitos: 908-724-552

Havendo dúvidas, contate o Prof. Alexandre Levine: alevin@if.usp.br



Desenvolvido por IFUSP