PRESSURE-DEPENDENCE OF TC IN TL2BA2CACU2O8 AT HYDROSTATIC PRESSURES TO 6 GPA

We report the results of experiments carried out on single crystals of Tl2Ba2CaCu2O8 under nearly hydrostatic pressure conditions to 6 GPa. The critical temperature, T(c), is observed to possess a non-linear pressure dependence. While the increase of T(c) with increasing oxygen concentration in YBa2Ca3O7-delta is consistent with the observation of increasing T(c) with increasing pressure, the Tl2Ba2CaCu2O8 system demonstrates an increasing T(c) with decreasing oxygen content, but has a positive dT(c)/dP at low pressures. This behavior is clearly inconsistent with the picture applied to the Y-BaCuO system. In all the present measurements the curvature is downward and, in fact, for one sample it actually decreases. A theoretical explanation based upon the strong-coupling Eliashberg form of the BCS theory is put forth to ex lain this effect.