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Weyl metal, flat band insulator and superconductivity in thin films

Seminář
Úterý, 21.05.2019 15:00

Přednášející: F.V. Kusmartsev (Department of Physics, Loughborough University, UK )
Místo: Na Slovance, přednáškový sál v přízemí
Pořadatelé: Oddělení teorie kondenzovaných látek
Abstract: The behaviour of recently discovered topological materials[1-6] has astonished the community by showing numerous amazing properties such as Quantum Spin Hall effect, ultra-high electron mobility, linear magnetoresistance and negative electron refraction to name a few.[3-6] Here we propose to grow topological materials from conventional semiconductors such as Germanium(Ge) and Gray Tin(a-Sn) using a standard electron beam deposition method. An extensive series of Ge/a-Sn/Ge multilayers has been produced, where unconventional Weyl metal(WM), topological insulator(TI) and superconductor(TS) states have been discovered. The WM phase is defined by two pairs of Weyl cones of opposite chirality; while the TI state is characterized by a flat band(FB) described by a non-zero Chern number. A topology driven metal-insulator transition arises between the WM and the flat band TI states at a critical thickness of the intermediate a-Sn film layer equal to 8.5 nm. Furthermore, at low temperatures, both the Weyl metal and TI phases condense into a superconducting state with TSC=7.0K, which has a likely topological origin associated with the flat band. Present findings reveal a new class of topological materials, which are protected by time reversal symmetry. They are bridging the gap between Weyl metals and topological insulators. The use of commercially viable components such as Sn, Ge or Si and the robustness of the multilayer synthesis processes promotes easy scaled up production, that may finally unlock the vast practical applications potential in these exceptional systems.

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[6] R. D. Y. Hills, A. Kusmartseva, and F. V. Kusmartsev, Phys. Rev. B 95, 214103 (2017).