Large Exchange Coupling Between Localized Spins and Topological Bands in MnBi2Te4

Hari Padmanabhan; Vladimir A. Stoica; Peter K. Kim; Maxwell Poore; Tiannan Yang; Xiaozhe Shen; Alexander H. Reid; Ming Fu Lin; Suji Park; Jie Yang; Huaiyu Wang; Nathan Z. Koocher; Danilo Puggioni; Alexandru B. Georgescu; Lujin Min; Seng Huat Lee; Zhiqiang Mao; James M. Rondinelli; Aaron M. Lindenberg; Long Qing Chen; Xijie Wang; Richard D. Averitt; John W. Freeland; Venkatraman Gopalan

doi:10.1002/adma.202202841

Large Exchange Coupling Between Localized Spins and Topological Bands in MnBi₂Te₄

Hari Padmanabhan^*, Vladimir A. Stoica, Peter K. Kim, Maxwell Poore, Tiannan Yang, Xiaozhe Shen, Alexander H. Reid, Ming Fu Lin, Suji Park, Jie Yang, Huaiyu Wang, Nathan Z. Koocher, Danilo Puggioni, Alexandru B. Georgescu, Lujin Min, Seng Huat Lee, Zhiqiang Mao, James M. Rondinelli, Aaron M. Lindenberg, Long Qing ChenXijie Wang, Richard D. Averitt, John W. Freeland, Venkatraman Gopalan^*

^*Corresponding author for this work

Materials Science and Engineering

Research output: Contribution to journal › Article › peer-review

12 Scopus citations

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.

Original language	English (US)
Article number	2202841
Journal	Advanced Materials
Volume	34
Issue number	49
DOIs	https://doi.org/10.1002/adma.202202841
State	Published - Dec 8 2022

Funding

H.P., V.A.S., H.W., P.K., M.P., N.Z.K., A.M.L., R.D.A., J.M.R., J.W.F., and V.G. acknowledge primary support from the DOE‐BES grant DE‐SC0012375. The computational efforts on the ultrafast electron scattering experiments and Landau‐Lifshitz‐Gilbert modeling of ultrafast spin dynamics were supported by the DOE‐BES Computational Materials Science program under grant number DE‐SC0020145 (H.P., T.Y., L‐Q.C., and V.G.). Support for crystal growth and characterization was provided by the National Science Foundation through the Penn State 2D Crystal Consortium‐Materials Innovation Platform (2DCC‐MIP) under NSF cooperative agreement DMR‐1539916. D.P. was supported by the Army Research Office (ARO) under grant no. W911NF‐15‐1‐0017. SLAC MeV‐UED is supported in part by the DOE BES SUF Division Accelerator & Detector R&D program, the LCLS Facility, and SLAC under Contract Nos. DE‐AC02–05‐CH11231 and DE‐AC02–76SF00515. S.P. acknowledges support from the Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under contract DE‐AC02‐76SF00515. This research used resources of the Advanced Photon Source, a Department of Energy Office of Science User Facility operated by Argonne National Laboratory under contract no. DE‐AC02‐06CH11357. H.P., V.A.S., H.W., P.K., M.P., N.Z.K., A.M.L., R.D.A., J.M.R., J.W.F., and V.G. acknowledge primary support from the DOE-BES grant DE-SC0012375. The computational efforts on the ultrafast electron scattering experiments and Landau-Lifshitz-Gilbert modeling of ultrafast spin dynamics were supported by the DOE-BES Computational Materials Science program under grant number DE-SC0020145 (H.P., T.Y., L-Q.C., and V.G.). Support for crystal growth and characterization was provided by the National Science Foundation through the Penn State 2D Crystal Consortium-Materials Innovation Platform (2DCC-MIP) under NSF cooperative agreement DMR-1539916. D.P. was supported by the Army Research Office (ARO) under grant no. W911NF-15-1-0017. SLAC MeV-UED is supported in part by the DOE BES SUF Division Accelerator & Detector R&D program, the LCLS Facility, and SLAC under Contract Nos. DE-AC02–05-CH11231 and DE-AC02–76SF00515. S.P. acknowledges support from the Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under contract DE-AC02-76SF00515. This research used resources of the Advanced Photon Source, a Department of Energy Office of Science User Facility operated by Argonne National Laboratory under contract no. DE-AC02-06CH11357.

Keywords

exchange coupling
itinerant magnetism
magnetic topological materials
nonequilibrium
ultrafast optics

ASJC Scopus subject areas

General Materials Science
Mechanics of Materials
Mechanical Engineering

Access to Document

10.1002/adma.202202841

Cite this

Padmanabhan, H., Stoica, V. A., Kim, P. K., Poore, M., Yang, T., Shen, X., Reid, A. H., Lin, M. F., Park, S., Yang, J., Wang, H., Koocher, N. Z., Puggioni, D., Georgescu, A. B., Min, L., Lee, S. H., Mao, Z., Rondinelli, J. M., Lindenberg, A. M., ... Gopalan, V. (2022). Large Exchange Coupling Between Localized Spins and Topological Bands in MnBi₂Te₄. Advanced Materials, 34(49), Article 2202841. https://doi.org/10.1002/adma.202202841

@article{585d5475355f4708a7134cb164535064,

title = "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.",

keywords = "exchange coupling, itinerant magnetism, magnetic topological materials, nonequilibrium, ultrafast optics",

author = "Hari Padmanabhan and Stoica, {Vladimir A.} and Kim, {Peter K.} and Maxwell Poore and Tiannan Yang and Xiaozhe Shen and Reid, {Alexander H.} and Lin, {Ming Fu} and Suji Park and Jie Yang and Huaiyu Wang and Koocher, {Nathan Z.} and Danilo Puggioni and Georgescu, {Alexandru B.} and Lujin Min and Lee, {Seng Huat} and Zhiqiang Mao and Rondinelli, {James M.} and Lindenberg, {Aaron M.} and Chen, {Long Qing} and Xijie Wang and Averitt, {Richard D.} and Freeland, {John W.} and Venkatraman Gopalan",

note = "Publisher Copyright: {\textcopyright} 2022 Wiley-VCH GmbH.",

year = "2022",

month = dec,

day = "8",

doi = "10.1002/adma.202202841",

language = "English (US)",

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Padmanabhan, H, Stoica, VA, Kim, PK, Poore, M, Yang, T, Shen, X, Reid, AH, Lin, MF, Park, S, Yang, J, Wang, H, Koocher, NZ, Puggioni, D, Georgescu, AB, Min, L, Lee, SH, Mao, Z, Rondinelli, JM, Lindenberg, AM, Chen, LQ, Wang, X, Averitt, RD, Freeland, JW & Gopalan, V 2022, 'Large Exchange Coupling Between Localized Spins and Topological Bands in MnBi₂Te₄', Advanced Materials, vol. 34, no. 49, 2202841. https://doi.org/10.1002/adma.202202841

TY - JOUR

T1 - Large Exchange Coupling Between Localized Spins and Topological Bands in MnBi2Te4

AU - Padmanabhan, Hari

AU - Stoica, Vladimir A.

AU - Kim, Peter K.

AU - Poore, Maxwell

AU - Yang, Tiannan

AU - Shen, Xiaozhe

AU - Reid, Alexander H.

AU - Lin, Ming Fu

AU - Park, Suji

AU - Yang, Jie

AU - Wang, Huaiyu

AU - Koocher, Nathan Z.

AU - Puggioni, Danilo

AU - Georgescu, Alexandru B.

AU - Min, Lujin

AU - Lee, Seng Huat

AU - Mao, Zhiqiang

AU - Rondinelli, James M.

AU - Lindenberg, Aaron M.

AU - Chen, Long Qing

AU - Wang, Xijie

AU - Averitt, Richard D.

AU - Freeland, John W.

AU - Gopalan, Venkatraman

PY - 2022/12/8

Y1 - 2022/12/8

N2 - 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.

AB - 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.

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KW - magnetic topological materials

KW - nonequilibrium

KW - ultrafast optics

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