Liu Yi, Wang Ziqiao, Shan Pujia, Tang Yue, Liu Chaofei, Chen Cheng, Xing Ying, Wang Qingyan, Liu Haiwen, Lin Xi, Xie X C, Wang Jian
International Center for Quantum Materials, School of Physics, Peking University, 100871, Beijing, China.
Collaborative Innovation Center of Quantum Matter, 100871, Beijing, China.
Nat Commun. 2019 Aug 12;10(1):3633. doi: 10.1038/s41467-019-11607-w.
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.
超导体 - 绝缘体/金属转变（SIT/SMT）代表了量子相变的一个原型，其中量子涨落起主导作用并显著改变低维超导系统的物理性质。最近对量子格里菲斯奇点（QGS）的观测为理解二维超导体中量子相变的微妙之处提供了一个重要视角。在此，我们研究了在极低温下超薄晶体铅膜中磁场诱导的SMT。当接近零温度量子临界点时观察到发散的临界指数，表明存在QGS。特别地，SMT的反常相边界，即在低温区域起始临界场随温度降低而减小，这使我们的观测与之前各种二维超导体中QGS的报道有所不同。我们证明这种反常相边界源于具有显著自旋 - 轨道相互作用的超薄铅膜中的超导涨落。我们的发现揭示了具有反常相边界的二维超导体中SMT的QGS的一个新方面。
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