Possibility of superconductivity at 65°C in Sr-Ba-Y-Cu-O system

Transition to a zero-resistance state at 65°C (338 K) was observd in a Sr-Ba-Y-Cu-O system for the first time. A nonlinear I-V characteristic curve was observed at that temperature. The resistivity changed from 5×10 -4 Ωcm to below a measurable limit of 1×10 -8 Ωcm between 71 and 65°C. The zero-resistance state reminiscent of superconductivity was continued for ten days at room temperature in air. A magnetization measurement indicated a very small volume fraction of the room temperature superconducting state, if any. X-ray diffractogram showed almost a single phase of oxygen-deficient perovskite with a trace of unidentified phase. Photoemission measurement showed the coexistence of multivalent Cu ions and a relatively low density of state at Fermi level. The superconductivity can be interpreted by the previously proposed d-hole mechanism.