High-pressure valence instability and Tc maximum in superconducting CeCu2Si2

Abstract

The high-pressure electrical resistivity of the Kondo compound ${\mathrm{CeCu}}_2$ ${\mathrm{Si}}_2$ was investigated down to the subkelvin temperature range. The main result is the occurrence of a valence transition associated with a steep increase of the superconducting critical temperature $T_c$ to about 2 K near 25 kbar. In the intermediate-valence phase, $\frac{\partial T_c}{\partial P}$ is negative, and no evidence for superconductivity is found above 1.2 K for $P>\mathrm{}100\mathrm{}$ kbar. At pressure of the order of 200 kbar, the $\rho \mathrm{}\left(T\right)\mathrm{}$ curves between 0 and 300 K are similar to those for ${\mathrm{LaCu}}_2$ ${\mathrm{Si}}_2$ at ambient pressure. The preceding results are discussed in terms of a two-component ($sd+f$) picture.