Strong-Coupling Superconductivity of CeIrSi₃ with the Non-centrosymmetric Crystal Structure

Abstract

We studied the pressure-induced superconductor CeIrSi₃ 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_c=2.25 GPa , where the antiferromagnetic state disappears. The heat capacity C_ac shows both antiferromagnetic and superconducting transitions at pressures close to P_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_sc=1.6 K around 2.5–2.7 GPa. At 2.58 GPa, a large heat capacity anomaly was observed at T_sc=1.59 K. The jump of the heat capacity in the form of ΔC_ac⁄C_ac(T_sc) is 5.7±0.1. This is the largest observed value among previously reported superconductors, indicating the strong-coupling superconductivity. The electronic specific heat coefficient at T_sc is, however, approximately unchanged as a function of pressure, even at P_c.