Pressure dependence of the superconducting critical temperature of HgBa2Ca2Cu3O8+y and HgBa2Ca3Cu4O10+y up to 30 GPa

Abstract

By performing experiments on samples as pure as presently available, the origin of the reported pressure-induced Tc values well above 150 K in the mercury-based high-Tc superconductors has been investigated. For HgBa2Ca2Cu3O8+y (Hg-1223) maximum Tc values between 142 K and 146 K are obtained under pressure up to 30 GPa, while for HgBa2Ca3Cu4O10+y (Hg-1234) Tc never exceeds 121 K. To verify the reproducibility between different laboratories the pressure dependence of a sample from the same batch as the sample on which Nuñez-Regueiro reported a Tc value of 157 K at 23.5 GPa has also been measured. Below 10 GPa the agreement with his results is rather good and a possible explanation for the disagreement above 10 GPa is given. It appears that the reported high Tc values in non-single-phase Hg-1223 samples are due to the presence of Hg-1234 phase impurities. Also some of the adopted definitions of Tc have led to somewhat optimistic values of Tc: The high-pressure results on Hg-1223 found in the literature are therefore reviewed and reanalyzed. © 1996 The American Physical Society.

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