Critical rf Magnetic Fields for Some Type-I and Type-II Superconductors

The critical rf magnetic field ${H_c}^{\mathrm{rf}}$ of several type-I and type-II superconductors has been measured between 90 and 300 MHz and near $T_c$ has been found to approach the ideal superheating field in nearly all cases. However, in the same samples the dc critical field shows little evidence of superheating. The temperature dependence of ${H_c}^{\mathrm{rf}}$ suggests that rf-stimulated vortex nucleation occurs in the type-I materials.