Large Itinerant Electron Exchange Coupling in the Magnetic Topological Insulator MnBi2Te4

Abstract

Magnetism in topological materials creates phases exhibiting quantized transport phenomena with applications in spintronics and quantum information. The emergence of such phases relies on strong interaction between localized spins and itinerant states comprising the topological bands, and the subsequent formation of an exchange gap. However, this interaction has never been measured in any intrinsic magnetic topological material. Using a multimodal approach, this exchange interaction is measured in MnBi2Te4, the first realized intrinsic magnetic topological insulator. Interrogating nonequilibrium spin dynamics, itinerant bands are found to exhibit a strong exchange coupling to localized Mn spins. Momentum-resolved ultrafast electron scattering and magneto-optic measurements reveal that itinerant spins disorder via electron-phonon scattering at picosecond timescales. Localized Mn spins, probed by resonant X-ray scattering, disorder concurrently with itinerant spins, despite being energetically decoupled from the initial excitation. Modeling the results using atomistic simulations, the exchange coupling between localized and itinerant spins is estimated to be >100 times larger than superexchange interactions. This implies an exchange gap of >25 meV should occur in the topological surface states. By directly quantifying local-itinerant exchange coupling, this work validates the materials-by-design strategy of utilizing localized magnetic order to create and manipulate magnetic topological phases, from static to ultrafast timescales.

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Cited by in corpus (13)

• Observation of the Axion quasiparticle in 2D MnBi${}_2$Te${}_4$
• Real-time observation of magnetization and magnon dynamics in a two-dimensional topological antiferromagnet MnBi2Te4
• On the topological surface states of the intrinsic magnetic topological insulator Mn-Bi-Te family
• Imaging the breakdown and restoration of topological protection in magnetic topological insulator MnBi${}_2$Te${}_4$
• Growth of bilayer stanene on a magnetic topological insulator aided by a buffer layer
• Distinguishing Surface and Bulk Electromagnetism via Their Dynamics in an Intrinsic Magnetic Topological Insulator
• Spin fractionalization in a Kondo-lattice superconductor heterostructure
• Antiferromagnetic order in a layered magnetic topological insulator MnBi${}_2$Se${}_4$ probed by resonant soft x-ray scattering
• Using magnetic dynamics to measure the spin gap in a candidate Kitaev material
• Magnetic Interactions and Cluster Formation: Boosting Surface Thermopower in Topological Insulators
• Ultrafast Magneto-optical Fingerprints of Altermagnetism in MnTe
• Research on topological materials using ultrafast spectroscopy
• Synthesis of intrinsic magnetic topological insulator MnBi2nTe3n+1 family by chemical vapor transport method with feedback regulation