Evidences for pressure-induced two-phase superconductivity and mixed structures of NiTe₂ and NiTe in type-II Dirac semimetal NiTe_(2-x) (x = 0.38 ± 0.09) single crystals

Creators: Feng, Z.; Si, J.; Li, T.; Dong, H.; Xu, C.; Yang, J.; Zhang, Z.; Wang, K.; Wu, H.; Hou, Q.; Xing, J.-J.; Wan, S.; Li, S.; Deng, W.; Feng, J.; Pal, A.; Chen, F.; Hu, S.; Ge, J.-Y.; Dong, C.; Wang, S.; Ren, W.; Cao, S.; Liu, Y.; Xu, X.; Zhang, J.; Chen, B.; Yeh, N.-C.

Abstract

Bulk NiTe₂ is a type-II Dirac semimetal with non-trivial Berry phases associated with the Dirac fermions. Theory suggests that monolayer NiTe₂ is a two-gap superconductor, whereas experimental investigation of bulk NiTe_(1.98) for pressures (P) up to 71.2 GPa do not reveal any superconductivity. Here we report experimental evidences for pressure-induced two-phase superconductivity as well as mixed structures of NiTe₂ and NiTe in Te-deficient NiTe_(2-x) (x = 0.38 ± 0.09) single crystals. Hole-dominant multi-band superconductivity with the P3¯m1 hexagonal-symmetry structure of NiTe₂ appears at P ≥ 0.5 GPa, whereas electron-dominant single-band superconductivity with the P2/m monoclinic-symmetry structure of NiTe emerges at 14.5 GPa < P < 18.4 GPa. The coexistence of hexagonal and monoclinic structures and two-phase superconductivity is accompanied by a zero Hall coefficient up to ∼ 40 GPa, and the second superconducting phase prevails above 40 GPa, reaching a maximum T_c = 7.8 K and persisting up to 52.8 GPa. Our findings suggest the critical role of Te-vacancies in the occurrence of superconductivity and potentially nontrivial topological properties in NiTe_(2-x).

Additional Information

© 2020 Elsevier. Received 5 December 2020, Revised 27 December 2020, Accepted 30 December 2020, Available online 18 January 2021. This work at the Shanghai University (SHU) is jointly supported by the Ministry of Science and Technology of the People's Republic of China No. (2020YFB0704503, 2016YFB0700201, 2018YFB0704400), National Natural Science Foundation of China (11774217, 11974061, U1732162, 10904088), Shanghai Pujiang Program (13PJD015), and Science and Technology commission of Shanghai Municipality (13ZR1415200). The research at the California Institute of Technology was supported by the National Science Foundation under the Institute for Quantum Information and Matter (award #1733907). N.-C. Yeh acknowledges the hospitality and sponsorship of her visit to the SHU under the Overseas Expert Recruitment Program at SHU. The authors thank both BL15U1 and BL14B1 beamlines at the SSRF for providing the beam time, and also thank Professor Patrick A. Lee from Massachusetts Institute of Technology for stimulating discussions. Credit author statement: Zhenjie Feng, Supervision, Conceptualization, Formal analysis, Investigation, Writing – review & editing, Visualization, Project administration, Funding acquisition. Jingying Si, Tao Li, Investigation, Visualization, Formal analysis, Writing – original draft. Hongliang Dong, Ke Wang, Hao Wu, Qiang Hou, JuanJuan Xing, Shun Wan, Shujia Li, Wen Deng, Jiajia Feng, Arnab Pal, Fei Chen, Jun-Yi Ge, Shenghao Wang, Data curation, Validation. Chunqiang Xu, Yi Liu, Xiaofeng Xu, Resources. Jiong Yang, Zhou Zhang, Shunbo Hu, Formal analysis, Software, Visualization. Cheng Dong, Wei Ren, Shixun Cao, Formal analysis. Jincang Zhang, Bin Chen, Funding acquisition, Project administration. Nai-Chang Yeh, Formal analysis, Investigation, Writing – review & editing, Project administration, Funding acquisition. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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