Anomalous quantum Griffiths singularity in ultrathin crystalline lead films

TL;DR

This study reveals an anomalous quantum Griffiths singularity in ultrathin crystalline lead films, showing unique phase boundary behavior linked to superconducting fluctuations, advancing understanding of quantum phase transitions in 2D superconductors.

Contribution

It reports the first observation of an anomalous phase boundary behavior associated with quantum Griffiths singularity in ultrathin Pb films, highlighting the role of superconducting fluctuations.

Findings

Divergent critical exponent indicating QGS near quantum critical point

Anomalous decrease of critical field with decreasing temperature

Superconducting fluctuations cause the observed phase boundary behavior

Abstract

We study the magnetic field induced superconductor-metal transition (SMT) in ultrathin crystalline Pb films. By performing ultralow temperature transport measurement, the divergent critical exponent as an indication of quantum Griffiths singularity (QGS) is observed when approaching zero temperature quantum critical point. Distinctively, the phase boundary of SMT exhibits an anomalous behavior in low temperature regime that the onset critical field decreases with decreasing temperatures, which distinguishes our observation from earlier reports of QGS in various two-dimensional superconductors. We demonstrate that this observed anomalous phase boundary has its origin from the superconducting fluctuations in ultrathin Pb films. Our findings reveal a novel aspect of the QGS of SMT in two-dimentional superconducting systems with anomalous phase boundary.