Pressure induced transformation of the superconducting state of underdopedLa1.985Sr0.015CuO4+delta (delta < 0.023)

We have studied the superconducting (sc.) transitions in La1.985Sr0.015CuO4 +delta by using different high-pressure techniques. At zero pressure the tr ansition is observed at 15 K for delta < 0.025 and at 30 K for <delta> > 0. 025. The application of hydrostatic pressure at: room temperature results i n a positive shift of T-c and a crossover from the 15 K to the 30 K state. At about 0.7 GPa the 30 K state quickly grows at the expense of the origina l 15 K state. If pressure is changed at low temperature (77 K) no such chan ge in the sc. state can be detected. The data are explained in terms of pre ssure-induced redistribution of oxygen and charge carriers.