Theory of Superconductivity in CeMIn5(M=Co, Rh, Ir) on the Basis of the Three Dimensional Periodic Anderson Model

Abstract

CeMIn 5 (M=Co, Rh, Ir) are heavy fermion compounds with a HoCoGa 5 -type structure. CeCoIn 5 and CeIrIn 5 become superconducting at ambient pressure with T c =2.3 and 0.4 K, respectively. On the other hand, CeRhIn 5 is an antiferromagnet at ambient pressure, and becomes superconducting under pressures greater than 1.6 GPa. Nuclear-quadrupole-resonance (NQR), thermal conductivity, specific heat, and electrical resistivity measurements indicate that the superconductivity in CeMIn 5 has line nodes. However, the pairing symmetry between d x 2 - y 2 and d x y is controversial based on the angle-dependent measurements of thermal conductivity and specific heat under the magnetic field, respectively. Therefore, we investigate the gap structure of CeMIn 5 by a detailed calculation. In order to reproduce the band structure characteristics of CeMIn 5 , we introduce a three-dimensional (3D) periodic Anderson model (PAM) and solve the Eliashberg equations. Thus, we identify the gap structure of CeMIn 5 as the d x 2 - y 2 symmetry. In addition, we discuss the pressure dependence of T c and show that two opposing factors determine T c . One factor is the momentum dependence of quasi-particle interaction and the other factor is the wave-function renormalization factor.