Abstract
MnBi2Te4 represents a new class of magnetic topological insulators in which novel quantum phases emerge at temperatures higher than those found in magnetically doped thin films. Here, we investigate how couplings between electron, spin, and lattice are manifested in the phonon spectra of few-septuple-layer thick MnBi2Te4. After categorizing phonon modes by their symmetries, we study the systematic changes in frequency, line width, and line shape of a spectrally isolated A1g mode. The electron-phonon coupling increases in thinner flakes as manifested in a broader phonon line width, which is likely due to changes of the electron density of states. In 4- and 5-septuple thick samples, the onset of magnetic order below the Néel temperature is concurrent with a transition to an insulating state. We observe signatures of a reduced electron-phonon scattering across this transition as reflected in the reduced Fano parameter. Finally, spin-lattice coupling is measured and modeled from temperature-dependent phonon frequency.
Original language | English |
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Pages (from-to) | 6139-6145 |
Number of pages | 7 |
Journal | Nano Letters |
Volume | 21 |
Issue number | 14 |
DOIs | |
State | Published - Jul 28 2021 |
Funding
We thank Chao Lei, B. Wieder, A. Ernst, and M. G. Vergniory for helpful discussions. This research was primarily supported by the National Science Foundation through the Center for Dynamics and Control of Materials: an NSF MRSEC under Cooperative Agreement No. DMR-1720595. The theory work was partially funded by NSF DMR-1949701. A.L. acknowledges support from the funding grant PID2019-105488GB-I00. Z.Y. and R.H. acknowledge support by the NSF CAREER Grant No. DMR-1760668. X.L. gratefully acknowledges the Welch Foundation grant F-1662 for support in sample preparation. M.R-V. acknowledges partial support by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, Condensed Matter Theory Program. Work at ORNL was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. L.J.C. and S.F.L. were primarily funded by the Ministry of Science and Technology 105-2112-M-001-031-MY3 in Taiwan. Partial funding for L.J.C. while visiting UT-Austin was provided by a Portugal-UT collaboration grant.
Keywords
- Raman spectroscopy
- electron-phonon interaction
- magnetic materials
- spin-lattice coupling
- topological materials
- van der Waals materials