THE SUPERCONDUCTING PHASES OF UPT3 UNDER PRESSURE

The upper critical field Hc2(T) of the heavy fermion superconductor UPt3 for a magnetic field applied in the basal plane has been studied down to 150 mK and under hydrostatic pressure up to 10 kbar. The kink already observed in Hc2(T) at ambient pressure disappears by applying a relatively low pressure. This suggests that the high-temperature low-field superconducting phase reported recently is rapidly suppressed by pressure. A possible interpretation of these results is discussed in connection with recent theories.