A topological Dirac insulator in a quantum spin Hall phase

By D. Hsieh, D. Qian, L. Wray, Y. Xia, Y. Hor, R. Cava, M. Zahid Hasan. Nature, 2008

2,781 citations recorded by the source corpus.

When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect dictates that an electronic excitation gap is generated in the sample bulk, but metallic conduction is permitted at the boundary. Recent theoretical models suggest that certain bulk insulators with large spin–orbit interactions may also naturally support conducting topological boundary states in the quantum limit, which opens up the possibility for studying unusual quantum Hall-like phenomena in zero external magnetic fields. Bulk Bi1-xSbx single crystals are predicted to be prime candidates for one such unusual Hall phase of matter known as the topological insulator. The hallmark of a topological insulator is the existence of metallic surface states that are higher-dimensional analogues of the edge states that characterize a quantum spin Hall insulator. In addition to its interesting boundary states, the bulk of Bi1-xSbx is predicted to exhibit three-dimensional Dirac particles, another topic of heightened current interest following the new findings in two-dimensional graphene and charge quantum Hall fractionalization observed in pure bismuth. However, despite numerous transport and magnetic measurements on the Bi1-xSbx family since the 1960s, no direct evidence of either topological Hall states or bulk Dirac particles has been found. Here, using incident-photon-energy-modulated angle-resolved photoemission spectroscopy (IPEM-ARPES), we report the direct observation of massive Dirac particles in the bulk of Bi0.9Sb0.1, locate the Kramers points at the sample’s boundary and provide a comprehensive mapping of the Dirac insulator’s gapless surface electron bands. These findings taken together suggest that the observed surface state on the boundary of the bulk insulator is a realization of the ‘topological metal’. They also suggest that this material has potential application in developing next-generation quantum computing devices that may incorporate ‘light-like’ bulk carriers and spin-textured surface currents.

Subfields: Atomic and Molecular Physics, and Optics, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/64a8e3e983920044aa4203be4815cf5ec63667cd

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Citations in the corpus

Recent developments in transport phenomena in Weyl semimetals (2013, background): “e bands in the sense of a 3D strong topological insulator. Therefore, it is possible to ﬁne tune Bi1−xSbxto the critical point separating the two phases (Fu and Kane [10], Murakami [25], Hsieh et al. [19]). The critical point has a single Dirac node in its bands structure. Kim et al. [20] applied a ”
Bulk-Edge Correspondence for Two-Dimensional Topological Insulators (2012, background): “They have been theoretically predicted as a class [16] and as a specific compound [2], in which the effect was then observed [15,19].”
Colloquium : Topological band theory (2016, background): “Among the practically realized materials, nontrivial compounds were first predicted theoretically before experimental verification, including Bi1-xSbx (Fu and Kane 2007; Hsieh et al. 2008) for Z2 phase (Sec.”
First principles design of spintronics materials (2016, background): “Typical examples of TIs are HgTe [14] and Bi1-xSbx [15].”
Topological insulators, topological superconductors and Weyl fermion semimetals: discoveries, perspectives and outlooks (2015, methodology): “This was done only via the ARPES measurements that for the first time demonstrated spin-momentum helical locking of the gaplessness of the electron states on the boundary, while the bulk bands are gapped and inverted via a topological phase transition [2, 20, 29, 30].”
Photonic Floquet topological insulators (2012, background): “Because the right-hand side of equation (3) is z-dependent, there are no static eigenmodes.”