Pressure tuning of superconductivity independent of disorder in Tl$_{2}$Ba$_{2}$CaCu$_{2}$O$_{8+\delta}$
Varying the superconducting transition temperature over a large scale of a cuprate superconductor is a necessary step for identifying the unsettled mechanism of superconductivity. Chemical doping or element substitution has been proven to be effective but also brings about lattice disorder. Such disorder can completely destroy superconductivity even at a fixed doping level. Pressure has been thought to be the most clean method for tuning superconductivity. However, pressure-induced increase of disorder was recognized from recent experiments. By choosing a disordered Tl$_{2}$Ba$_{2}$CaCu$_{2}$O$_{8+\delta}$ at the optimal doping, we perform single-crystal x-ray diffraction and magnetic susceptibility measurements at high pressures. The obtained structural data provides evidence for the robust feature for the disorder of this material in the pressure range studied. This feature ensures the pressure effects on superconductivity distinguishable from the disorder. The derived parabolic-like behavior of the transition temperature with pressure up to near 30 GPa, having a maximum around 7 GPa, offers a platform for testing any realistic theoretical models in a nearly constant disorder environment. Such a behavior can be understood when considering the carrier concentration and the pairing interaction strength as two pressure intrinsic variables.