Effect of Pressure on the Superconducting Transition Temperature in Mercury-Based Cuprates

The pressure dependence of the transition temperature of the mercury-based cuprates is analyzed through a phenomenological model, based on the inverted parabolic relation between the critical temperature (T_c) and the hole concentration per CuO₂ layer (n). It is found that another inverted parabolic relation between the pressure dependence of the superconducting transition temperature at the optimum hole concentration and the pressure fit the recent experimental results of the mercury-based superconductors. This relation leads to a universal relation that is obeyed not only by mercury-based cuprates but also by many other high T_c compounds. In contrast to earlier studies, the transition temperature at pressure p (T_c(p)) is always less than the transition temperature for the optimum hole concentration (T^op_c(p)) in agreement with the experiment. The effect of the pressure-induced change in the hole concentration on the transition temperature is found to be small compared to the intrinsic effects.