Evidence for nematic superconductivity of topological surface states in PbTaSe2

Tian Le; Yue Sun; Hui-Ke Jin; Liqiang Che; Lichang Yin; Jie Li; Guiming Pang; Chunqiang Xu; Lingxiao Zhao; Shunichiro Kittaka; Toshiro Sakakibara; Kazushige Machida; Raman Sankar; Huiqiu Yuan; Genfu Chen; Xiaofeng Xu; Shiyan Li; Yi Zhou; Xin Lu

doi:10.1016/j.scib.2020.04.039

Evidence for nematic superconductivity of topological surface states in PbTaSe₂

Sci Bull (Beijing). 2020 Aug 30;65(16):1349-1355. doi: 10.1016/j.scib.2020.04.039. Epub 2020 Apr 30.

Authors

Tian Le¹, Yue Sun², Hui-Ke Jin³, Liqiang Che¹, Lichang Yin¹, Jie Li¹, Guiming Pang¹, Chunqiang Xu⁴, Lingxiao Zhao⁵, Shunichiro Kittaka⁶, Toshiro Sakakibara⁶, Kazushige Machida⁷, Raman Sankar⁸, Huiqiu Yuan⁹, Genfu Chen¹⁰, Xiaofeng Xu¹¹, Shiyan Li¹², Yi Zhou¹³, Xin Lu¹⁴

Affiliations

¹ Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China.
² Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara 252-5258, Japan. Electronic address: sunyue@phys.aoyama.ac.jp.
³ Department of Physics, Zhejiang University, Hangzhou 310027, China.
⁴ Department of Applied Physics, Zhejiang University of Technology, Hangzhou 310023, China.
⁵ Beijing National Laboratory for Condensed Matter Physics & Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
⁶ Institute for Solid State Physics (ISSP), The University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
⁷ Department of Physics, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
⁸ Institute of Physics, Academia Sinica, Nankang, Taipei 11529, Taiwan, China.
⁹ Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China; Zhejiang Province Key Laboratory of Quantum Technology and Device, Zhejiang University, Hangzhou 310027, China; Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
¹⁰ Beijing National Laboratory for Condensed Matter Physics & Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; Collaborative Innovation Center of Quantum Matter, Beijing 100084, China.
¹¹ Department of Applied Physics, Zhejiang University of Technology, Hangzhou 310023, China. Electronic address: xuxiaofeng@zjut.edu.cn.
¹² State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China; Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
¹³ Beijing National Laboratory for Condensed Matter Physics & Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China; Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China; Department of Physics, Zhejiang University, Hangzhou 310027, China.
¹⁴ Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China; Zhejiang Province Key Laboratory of Quantum Technology and Device, Zhejiang University, Hangzhou 310027, China; Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China. Electronic address: xinluphy@zju.edu.cn.

PMID: 36659213
DOI: 10.1016/j.scib.2020.04.039

Abstract

Spontaneous symmetry breaking has been a paradigm to describe the phase transitions in condensed matter physics. In addition to the continuous electromagnetic gauge symmetry, an unconventional superconductor can break discrete symmetries simultaneously, such as time reversal and lattice rotational symmetry. In this work we report a characteristic in-plane 2-fold behaviour of the resistive upper critical field and point-contact spectra on the superconducting semimetal PbTaSe₂ with topological nodal-rings, despite its hexagonal lattice symmetry (or D_3h in bulk while C_3v on surface, to be precise). The 2-fold behaviour persists up to its surface upper critical field H_c2^R even though bulk superconductivity has been suppressed at its bulk upper critical field H_c2^HC≪H_c2^R, signaling its probable surface-only electronic nematicity. In addition, we do not observe any lattice rotational symmetry breaking signal from field-angle-dependent specific heat within the resolution. It is worth noting that such surface-only electronic nematicity is in sharp contrast to the observation in the topological superconductor candidate, Cu_xBi₂Se₃, where the nematicity occurs in various bulk measurements. In combination with theory, superconducting nematicity is likely to emerge from the topological surface states of PbTaSe₂, rather than the proximity effect. The issue of time reversal symmetry breaking is also addressed. Thus, our results on PbTaSe₂ shed new light on possible routes to realize nematic superconductivity with nontrivial topology.

Keywords: Nematic superconductivity; Point-contact spectroscopy; Topological superconductor; Topological surface states.