Magnetic-field-induced pair-breaking effects in granular Pb films near the superconductor-to-insulator transition

We have measured the magnetic-field dependence, 0≤H≤8 T, of the resistive transitions R(T) of ultrathin granular superconducting Pb films with normal-state sheet resistances, ${\mathit{R}}_{\mathit{Q}}$≤${\mathit{R}}_{\mathit{N}}$≤100 kΩ, where ${\mathit{R}}_{\mathit{Q}}$=h/4${\mathit{e}}^2$≃6.45 kΩ. The data suggest that the magnetic-field-induced superconductor-to-insulator transition in these films occurs in a field regime where pair-breaking effects have significantly reduced the amplitude of the superconducting order parameter. We compare our results with those obtained on systems with uniform morphologies.