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.
T. Asaba and B. J. Lawson and C. Tinsman and L. Chen and P. Corbae and G. Li and Y. Qiu and Y. S. Hor and L. Fu and L. Li, "Rotational Symmetry Breaking in a Trigonal Superconductor Nb-Doped Bi₂Se₃," Physical Review X, vol. 7, no. 1, American Physical Society (APS), Jan 2017.
The definitive version is available at https://doi.org/10.1103/PhysRevX.7.011009
Keywords and Phrases
Superconductivity; Topological Insulatorsy
International Standard Serial Number (ISSN)
Article - Journal
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01 Jan 2017
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.