Theoretical study on superconductivity in CeMIn(5) (M = Co, Rh, Ir): pairing symmetry and pressure dependence.

We study theoretically heavy fermion superconductors CeMIn(5) (M = Co, Rh, Ir). CeCoIn(5) and CeIrIn(5) that become superconducting at ambient pressure with T(c) = 2.3 K 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. With regards to the superconductivity, the existence of line nodes is indicated by nuclear-quadrupole-resonance (NQR), thermal conductivity, specific heat and electrical resistivity measurements. However, the pairing symmetry between d(x(2)-y(2)) and d(xy) is controversial. Therefore, we investigate the gap structure of CeMIn(5) by a detailed calculation. We introduce a three-dimensional periodic Anderson model (3D-PAM) in order to reproduce the band characteristics of CeMIn(5). Thus, we identify the gap structure of CeMIn(5) as the d(x(2)-y(2)) symmetry by solving the Èliashberg equations. In addition, we discuss the pressure dependence of T(c) and show that two factors determine T(c). One factor is the momentum dependence of quasi-particle interaction and the other factor is the wavefunction renormalization factor. Thus, we have explained the superconductivity in CeMIn(5) using the Fermi liquid theory.