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Author: Isaeva, A. × Subject: Topology ×

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    Possible experimental realization of a basic Z 2 topological semimetal in GaGeTe
    (College Park, MD : American Institute of Physics, 2019) Haubold, E.; Fedorov, A.; Pielnhofer, F.; Rusinov, I.P.; Menshchikova, T.V.; Duppel, V.; Friedrich, D.; Weihrich, R.; Pfitzner, A.; Zeugner, A.; Isaeva, A.; Thirupathaiah, S.; Kushnirenko, Y.; Rienks, E.; Kim, T.; Chulkov, E.V.; Büchner, B.; Borisenko, S.
    We report experimental and theoretical evidence that GaGeTe is a basic Z2 topological semimetal with three types of charge carriers: bulk-originated electrons and holes as well as surface state electrons. This electronic situation is qualitatively similar to the classic 3D topological insulator Bi2Se3, but important differences account for an unprecedented transport scenario in GaGeTe. High-resolution angle-resolved photoemission spectroscopy combined with advanced band structure calculations show a small indirect energy gap caused by a peculiar band inversion at the T-point of the Brillouin zone in GaGeTe. An energy overlap of the valence and conduction bands brings both electron and holelike carriers to the Fermi level, while the momentum gap between the corresponding dispersions remains finite. We argue that peculiarities of the electronic spectrum of GaGeTe have a fundamental importance for the physics of topological matter and may boost the material's application potential.
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    Topological Electronic Structure and Intrinsic Magnetization in MnBi4Te7: A Bi2Te3 Derivative with a Periodic Mn Sublattice
    (College Park, MD : American Physical Society, 2019) Vidal, R.C.; Zeugner, A.; Facio, J.I.; Ray, R.; Haghighi, M.H.; Wolter, A.U.B.; Corredor, Bohorquez, L.T.; Caglieris, F.; Moser, S.; Figgemeier, T.; Peixoto, T.R.F.; Vasili, H.B.; Valvidares, M.; Jung, S.; Cacho, C.; Alfonsov, A.; Mehlawat, K.; Kataev, V.; Hess, C.; Richter, M.; Büchner, B.; Van Den Brink, J.; Ruck, M.; Reinert, F.; Bentmann, H.; Isaeva, A.
    Combinations of nontrivial band topology and long-range magnetic order hold promise for realizations of novel spintronic phenomena, such as the quantum anomalous Hall effect and the topological magnetoelectric effect. Following theoretical advances, material candidates are emerging. Yet, so far a compound that combines a band-inverted electronic structure with an intrinsic net magnetization remains unrealized. MnBi2Te4 has been established as the first antiferromagnetic topological insulator and constitutes the progenitor of a modular (Bi2Te3)n(MnBi2Te4) series. Here, for n=1, we confirm a nonstoichiometric composition proximate to MnBi4Te7. We establish an antiferromagnetic state below 13 K followed by a state with a net magnetization and ferromagnetic-like hysteresis below 5 K. Angle-resolved photoemission experiments and density-functional calculations reveal a topologically nontrivial surface state on the MnBi4Te7(0001) surface, analogous to the nonmagnetic parent compound Bi2Te3. Our results establish MnBi4Te7 as the first band-inverted compound with intrinsic net magnetization providing a versatile platform for the realization of magnetic topological states of matter.