The critical fields of superconducting palladium hydride

The upper critical field of superconducting PdH x (x = H/Pd) is measured for a range of hydrogen concentrations (0.88 < x < 0.97). The upper critical field is found to increase linearly with decreasing temperature over the temperature range investigated (1.5 K < T < 7.5 K). The data are analyzed to obtain the critical field at zero temperature as a function of concentration. The data indicate two regimes: at low ( x < 0.92) concentrations the upper critical field increases rapidly with concentration while for higher ( x > 0.92) concentrations it is almost independent of concentration. It is suggested that the lower concentration PdH x may be a mixed phase system.