High pressure effects revisited for the cuprate superconductor family with highest critical temperature

How to enhance the superconducting critical temperature (T(c)) has been a primary issue since the discovery of superconductivity. The highest T(c) reported so far is 166 K in HgBa(2)Ca(2)Cu(3)O(8+δ) (Hg1223) at high pressure of 23 GPa, as determined with the reduction onset, but not zero, of resistivity. To clarify the possible condition of the real maximum T(c), it is worth revisiting the effects of pressure on T(c) in the highest T(c) family. Here we report a systematic study of the pressure dependence of T(c) in HgBa(2)CaCu(2)O(6+δ) (Hg1212) and Hg1223 with the doping level from underdoped to overdoped. The T(c) with zero resistivity is probed with a cubic-anvil-type apparatus that can produce hydrostatic pressures. Variation, not only increase but also decrease, of T(c) in Hg1212 and Hg1223 with pressure strongly depends on the initial doping levels. In particular, we confirm a maximum T(c) of 153 K at 22 GPa in slightly underdoped Hg1223.