posted on 2023-11-15, 16:05authored byHaoran Lu, Run Long, Wei-Hai Fang
Ultrafast charge and spin dynamics
have immense effects on the
applications of topological insulators (TIs). By performing spin-adiabatic
nonadiabatic molecular dynamics simulations in the presence of electron–phonon
(e-ph) and spin–phonon couplings,
we investigate temperature-dependent intra- and interband charge and
spin relaxation dynamics via the bulk and surface paths in the three-dimensional
TI Bi2Te3. The e-ph coupling dominates charge relaxation in the bulk path, and the relaxation
rate is positively correlated with temperature due to the large energy
gaps and weak spin polarization. Conversely, the relaxation dynamics
exhibits an opposite temperature dependence in the surface path because
of electron re-excitation and spin mismatching induced by spin–phonon
coupling, which arises from small energy gaps and strong spin polarization.
The two mechanisms rationalize the charge carriers being long-lived
in the bulk and surface phases at low and room temperature, respectively.
Additionally, strong thermal fluctuations of the topological states’
magnetic moments destroy the spin-momentum locking and trigger backscattering
at room temperature.