The search for unconventional superconductivity has been focused on materials with strong spin-orbit coupling and unique crystal lattices. Doped bismuth selenide (Bi2Se3) is a strong candidate, given the topological insulator nature of the parent compound and its triangular lattice. The coupling between the physical properties in the superconducting state and its underlying crystal symmetry is a crucial test for unconventional superconductivity. In this paper, we report direct evidence that the superconducting magnetic response couples strongly to the underlying trigonal crystal symmetry in the recently discovered superconductor with trigonal crystal structure, niobium (Nb)-doped Bi2Se3. As a result, the in-plane magnetic torque signal vanishes every 60°. More importantly, the superconducting hysteresis loop amplitude is enhanced along one preferred direction, spontaneously breaking the rotational symmetry. This observation indicates the presence of nematic order in the superconducting ground state of Nb-doped Bi2Se3.




This work is mainly supported by the Department of Energy (DOE) under Grant No. DE-SC0008110 (magnetization measurement), by the National Science Foundation (NSF) under Grant No. DMR-1255607 (sample growth), and by the David and Lucile Packard Foundation (theory). Supporting measurements were made possible with by the Office of Naval Research through Grant No. N00014-15-1-2382 (thermodynamic characterization), by the NSF under Grant No. 1307744 (electrical transport characterization), and by the NSF Major Research Instrumentation under Grant No. DMR-1428226 (supports the equipment of the thermodynamic and electrical transport characterizations). Some experiments were performed at the National High Magnetic Field Laboratory (NHMFL), which is supported by NSF Cooperative Agreement No. DMR-084173, by the State of Florida, and by the DOE.

Keywords and Phrases

Superconductivity; Topological Insulatorsy

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Publication Date

01 Jan 2017

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