Strong-Coupling Superconductivity of CeIrSi${}_3$ with the Non-centrosymmetric Crystal Structure

Abstract

We studied the pressure-induced superconductor CeIrSi${}_3$ with the non-centrosymmetric tetragonal structure under high pressure. The electrical resistivity and ac heat capacity were measured in the same run for the same sample. The critical pressure was determined to be $P_{\mathrm{c}}$ = 2.25 GPa, where the antiferromagnetic state disappears. The heat capacity $C_{\mathrm{ac}}$ shows both antiferromagnetic and superconducting transitions at pressures close to $P_{\mathrm{c}}$. On the other hand, the superconducting region is extended to high pressures of up to about 3.5 GPa, with the maximum transition temperature $T_{\mathrm{sc}}$ = 1.6 K around $2.5-2.7$ GPa. At 2.58 GPa, a large heat capacity anomaly was observed at $T_{\mathrm{sc}}$ = 1.59 K. The jump of the heat capacity in the form of $\Delta C_{\mathrm{ac}}/C_{\mathrm{ac}}(T_{\mathrm{sc}})$ is 5.7 $\pm$ 0.1. This is the largest observed value among previously reported superconductors, indicating the strong-coupling superconductivity. The electronic specific heat coefficient at $T_{\mathrm{sc}}$ is, however, approximately unchanged as a function of pressure, even at $P_{\mathrm{c}}$.

This paper will be published in J. Phys. Soc. Jpn. on the August issue of 2007

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