PRESSURE-INDUCED INSTABILITY IN THE TRANSITION-TEMPERATURE OF TL2BA2CUO6-CRYSTALS(DELTA SINGLE)

A pressure-induced time dependence of the superconducting transition t emperature has been observed and carefully examined in Tl2Ba2CuO6+delt a single crystals. The results strongly suggest a structure with two m etastable states, one of which is more stable at ambient pressure whil e the other is more stable above approximately 6 kbar. Assuming that t he excess interstitial oxygen O(4) is responsible for the metastable c hange, consistent with the path dependence of T(c) in pressure-tempera ture space discovered by Sieburger and Schilling, the activation energ y between the two metastable states of O(4) is estimated to be approxi mately 1 eV. A possible mechanism of the two states is proposed.