Pressure-Induced Superconducting Phase Separation in Oxygen-Doped La2-xSrxCuO4+δ

Abstract

The pressure effect on the superconducting transitions in La2-xSrxCuO4+δ is investigated by ac susceptibility measurements up to 2 GPa. Two series of samples with x=0 and x=0.015 and 0<δ<0.11 are compared with respect to the ambient and high pressure properties. At ambient pressure both sets of samples fit into the same phase diagram as a function of the total hole concentration (Sr– and oxygen doping contribute to the total carrier density, p). A single superconducting transition (Tc≈30 K) for p<0.085 splits into two transitions (Tc≈15 K and 30 K) at higher hole density indicating that electronic phase separation sets in above p=0.085. The pressure effect on Tc of the 30 K transition is unusually large, dTc (30)/dP≈10 K/GPa. The electronic phase separation at higher hole density is enhanced by pressure and Tc of the 15 K superconducting state exhibits a negative pressure shift, dTc (15)/dP≈-4 K/GPa. At a hole density close to 0.085 the electronic phase separation into the two superconducting states can be induced by pressure. The results are interpreted in terms of a strong correlation of the hole system and the interstitial (mobile) oxygen ions. Pressure, applied at ambient temperature, causes a redistribution of holes and oxygen and enhances superconductivity (Tc) as well as the tendency to phase separation.