Large enhancement of Tc (50K) by applying high pressure in the Hg-2212 superconductor

Abstract We have measured the resistance as a function of temperature under pressure up to 22GPa for samples of the bi-Hg-layer compound, Hg 2 Ba 2 ( Y 1− x Ca x ) Cu 2 O 8− d . We report here the largest total pressure effect ever observed in the superconducting critical temperature (> 50K over a span of 20GPa, independently of the Ca doping). We analyze our results on the basis of a phenomenological model founded on the Tc dependence with carrier density, generalized to include pressure. The large pressure effect observed in all Hg-based cuprates reveals the existence of a common hidden clue, whose identification is essential to stabilize at ambient pressure the structural arrangement responsible for the higher Tc's. This clue should also explain why the Hg-bearing superconductors are so susceptible to pressure.