Large Exchange Coupling Between Localized Spins and Topological Bands in MnBi2Te4
Abstract
Magnetism in topological materials creates phases exhibiting quantized transport phenomena with potential technological applications. The emergence of such phases relies on strong interaction between localized spins and the topological bands, and the consequent formation of an exchange gap. However, this remains experimentally unquantified in intrinsic magnetic topological materials. Here, this interaction is quantified in MnBi2Te4, a topological insulator with intrinsic antiferromagnetism. This is achieved by optically exciting Bi‐Te p states comprising the bulk topological bands and interrogating the consequent Mn 3d spin dynamics, using a multimodal ultrafast approach. Ultrafast electron scattering and magneto‐optic measurements show that the p states demagnetize via electron‐phonon scattering at picosecond timescales. Despite being energetically decoupled from the optical excitation, the Mn 3d spins, probed by resonant X‐ray scattering, are observed to disorder concurrently with the p spins. Together with atomistic simulations, this reveals that the exchange coupling between localized spins and the topological bands is at least 100 times larger than the superexchange interaction, implying an optimal exchange gap of at least 25 meV in the surface states. By quantifying this exchange coupling, this study validates the materials‐by‐design strategy of utilizing localized magnetic order to manipulate topological phases, spanning static to ultrafast timescales.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Nov 02, 2022
- Source ID
- 10.1002/adma.202202841
Entities
People
- Aaron M Lindenberg
- Alexander H. Reid
- Alexandru B. Georgescu
- Danilo Puggioni
- Haricharan Padmanabhan
- Huaiyu (hugo) Wang
- James M. Rondinelli
- Jie Yang
- John W Freeland
- Long‐qing Chen
- Lujin Min
- Maxwell Poore
- Ming‐fu Lin
- Nathan Z. Koocher
- Peter K. Kim
- Richard D. Averitt
- Seng Huat Lee
- Suji Park
- Tiannan Yang
- Venkatraman Gopalan
- Vladimir A. Stoica
- Xiaozhe Shen
- Xijie Wang
- Zhiqiang Mao
Organizations
- Argonne National Laboratory
- Army Research Office
- National Science Foundation
- Northwestern University
- Pennsylvania State University
- SLAC National Accelerator Laboratory
- Stanford University
- University of California, San Diego