Transport Measurements Of In-Plane Critical Fields In Yba2cu3o7-Delta To 300t

Thin-film YBa2Cu3O7-delta has been studied with in-plane magnetic fields B to 850 T, with good signal-to-noise to 300 T, using a GHz-transmission-line technique for electrical transport measurements in explosive-driven microsecond pulsed magnetic fields. At an ambient temperature of 1.6 K with B perpendicular to c axis we find an onset of dissipation at 150 T, the highest field reported, with a saturation of resistivity at 240 T. Comparison with the Pauli limit B-p = 155 T expected for this material suggests that the critical field is limited by spin paramagnetism.