Van der Waals Engineering of Ultrafast Carrier Dynamics in Magnetic Heterostructures
Paulina Majchrzak, Yuntian Liu, Klara Volckaert, Deepnarayan Biswas, Chakradhar Sahoo, Denny Puntel, Wibke Bronsch, Manuel Tuniz, Federico Cilento, Xingchen Pan, Qihang Liu, Yong P. Chen, Søren Ulstrup
Abstract
Heterostructures composed of the intrinsic magnetic topological insulator MnBi 2 Te 4 and its nonmagnetic counterpart Bi 2 Te 3 host distinct surface electronic band structures depending on the stacking order and exposed termination. Here, we probe the ultrafast dynamical response of MnBi 2 Te 4 and MnBi 4 Te 7 following near-infrared optical excitation using time- and angle-resolved photoemission spectroscopy and disentangle surface from bulk dynamics based on density functional theory slab calculations of the surface-projected electronic structure. We gain access to the out-of-equilibrium charge carrier populations of both MnBi 2 Te 4 and Bi 2 Te 3 surface terminations of MnBi 4 Te 7, revealing an instantaneous occupation of states associated with the Bi 2 Te 3 surface layer followed by carrier extraction into the adjacent MnBi 2 Te 4 layers with a laser fluence-tunable delay of up to 350 fs. The ensuing thermal relaxation processes are driven by phonon scattering with significantly slower relaxation times in the magnetic MnBi 2 Te 4 septuple layers. The observed competition between interlayer charge transfer and intralayer phonon scattering demonstrates a method to control ultrafast charge transfer processes in MnBi 2 Te 4 -based van der Waals compounds.