Anomalous quantum Griffiths singularity in ultrathin crystalline lead films

Yi Liu; Ziqiao Wang; Pujia Shan; Yue Tang; Chaofei Liu; Cheng Chen; Ying Xing; Qingyan Wang; Haiwen Liu; Xi Lin; X C Xie; Jian Wang

doi:10.1038/s41467-019-11607-w

Anomalous quantum Griffiths singularity in ultrathin crystalline lead films

Nat Commun. 2019 Aug 12;10(1):3633. doi: 10.1038/s41467-019-11607-w.

Authors

Yi Liu^{1

2}, Ziqiao Wang^{1

2}, Pujia Shan^{1

2}, Yue Tang^{1

2}, Chaofei Liu^{1

2}, Cheng Chen^{1

2}, Ying Xing^{1

2}, Qingyan Wang^{1

2}, Haiwen Liu³, Xi Lin^{1

2}, X C Xie^{1

2}, Jian Wang^{4

5

6

7}

Affiliations

¹ International Center for Quantum Materials, School of Physics, Peking University, 100871, Beijing, China.
² Collaborative Innovation Center of Quantum Matter, 100871, Beijing, China.
³ Center for Advanced Quantum Studies, Department of Physics, Beijing Normal University, 100875, Beijing, China. haiwen.liu@bnu.edu.cn.
⁴ International Center for Quantum Materials, School of Physics, Peking University, 100871, Beijing, China. jianwangphysics@pku.edu.cn.
⁵ Collaborative Innovation Center of Quantum Matter, 100871, Beijing, China. jianwangphysics@pku.edu.cn.
⁶ CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, 100190, Beijing, China. jianwangphysics@pku.edu.cn.
⁷ Beijing Academy of Quantum Information Sciences, 100193, Beijing, China. jianwangphysics@pku.edu.cn.

Abstract

Superconductor-insulator/metal transition (SIT/SMT) represents a prototype of quantum phase transition, where quantum fluctuation plays a dominant role and dramatically changes the physical properties of low-dimensional superconducting systems. Recent observation of quantum Griffiths singularity (QGS) offers an essential perspective to understand the subtleties of quantum phase transition in two-dimensional superconductors. Here we study the magnetic field induced SMT in ultrathin crystalline Pb films down to ultralow temperatures. The divergent critical exponent is observed when approaching zero temperature quantum critical point, indicating QGS. Distinctively, the anomalous phase boundary of SMT that the onset critical field decreases with decreasing temperatures in low temperature regime distinguishes our observation from previous reports of QGS in various two-dimensional superconductors. We demonstrate that the anomalous phase boundary originates from the superconducting fluctuations in ultrathin Pb films with pronounced spin-orbit interaction. Our findings reveal a novel aspect of QGS of SMT in two-dimensional superconductors with anomalous phase boundary.