Pressure-Induced Instability In The Transition-Temperature Of Tl2ba2cuo6+Delta Single-Crystals

A pressure-induced time dependence of the superconducting transition temperature has been observed and carefully examined in Tl2Ba2CuO6+delta single crystals. The results strongly suggest a structure with two metastable states, one of which is more stable at ambient pressure while the other is more stable above approximately 6 kbar. Assuming that the excess interstitial oxygen O(4) is responsible for the metastable change, consistent with the path dependence of T(c) in pressure-temperature space discovered by Sieburger and Schilling, the activation energy between the two metastable states of O(4) is estimated to be approximately 1 eV. A possible mechanism of the two states is proposed.