Van der Waals engineering of ultrafast carrier dynamics in magnetic heterostructures

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.

arXiv commentThis 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 © 2023 American Chemical Society after peer review. To access the final edited and published work see https://doi.org/10.1021/acs.nanolett.2c03075

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• Ultrafast Carrier Relaxation Dynamics in a Nodal-Line Semimetal PtSn${}_4$
• Distinguishing Surface and Bulk Electromagnetism via Their Dynamics in an Intrinsic Magnetic Topological Insulator
• Exploring Intrinsic Magnetic Topological Insulators: The Case of EuIn${}_2$As${}_2$