Experimental determination of the B-T phase diagram of YBa2Cu3O7-delta to 150 T for B perpendicular to c

The B-T phase diagram for thin film YBa2Cu3O7-delta with B parallel to the superconducting layers has been constructed from GHz transport measurements to 150 T. Up to 110 T the upper critical field is found to be linear in T and in remarkable agreement with extrapolation of the longstanding result o f Welp et al. arising from magnetization measurements to 6 T. Beyond this a departure from linear behavior occurs at T = 74 K, consistent with previou s low-temperature data. Evidence for a transition from a high-T regime domi nated by orbital effects, to a low-T regime, where paramagnetic limiting dr ives the quenching of superconductivity, is seen.