Pressure studies on the pseudogap and critical temperatures of a high-$T_c$ superconductor

We report simultaneous hydrostatic pressure studies on the critical temperature $T_c$ and on the pseudogap temperature $T^{*}$ performed through resistivity measurements on an optimally doped high-$T_c$ oxide ${\mathrm{Hg}}_{0.82}{\mathrm{Re}}_{0.18}{\mathrm{Ba}}_2{\mathrm{Ca}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{8+\delta }.$ The resistivity is measured as a function of the temperature for several different applied pressures around 1 GPa. We find that $T^{*}$ increases linearly with the pressure at a larger rate than $T_c.$ This result demonstrates that the well known intrinsic pressure effect on $T_c$ is more important at the pair formation temperature $T^{*}.$