Fig. 3

Anomalous quantum Griffiths singularity (QGS) of superconductor–metal transition (SMT) in 3.5-monolayer (ML) Pb film. a R_s(T) curves at various magnetic fields show SMT and reentrant behavior. b R_s(B) curves measured in the temperature region from 0.4 to 1.8 K. c The crossing points from neighboring R_s(B) curves and the onset T_c from R_s(T) curves determine the phase boundary of SMT. The phase boundary abnormally bends down at lower temperatures. d Scaling analysis indicates anomalous QGS behavior in 3.5-ML Pb film. The critical exponent diverges as \(z\nu \propto |B - B_{\mathrm{c}}^ \ast |^{ - 0.6}\) with temperature approaching zero and magnetic field tending to \(B_{\mathrm{c}}^ \ast\)