paper

Van der Waals engineering of ultrafast carrier dynamics in magnetic heterostructures

arXiv:2208.04098 · doi:10.1021/acs.nanolett.2c03075

Abstract

Heterostructures composed of the intrinsic magnetic topological insulator MnBi $_{2}$ Te $_{4}$ and its non-magnetic 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.

This document (21 pages, 4 figures) is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Lett. 2023, 23, 2, 414-421, Copyright Â© 2023 American Chemical Society after peer review. To access the final edited and published work see https://doi.org/10.1021/acs.nanolett.2c03075