NMR and NQR studies of the heavy fermion superconductorsCeTIn5 (T=Coand Ir)

Abstract

We have carried out ${}^{115}\mathrm{In}$ and ${}^{59}\mathrm{Co}$ nuclear quadrupole resonance and nuclear magnetic resonance measurements on ${\mathrm{CeCoIn}}_{5}$ and ${\mathrm{CeIrIn}}_{5}.$ The temperature T dependence of the nuclear spin-lattice relaxation rate ${1/T}_{1}$ of ${}^{115}\mathrm{In}$ in the normal state indicates that ${\mathrm{CeCoIn}}_{5}$ is located just at an antiferromagnetic instability, and ${\mathrm{CeIrIn}}_{5}$ is in the nearly antiferromagnetic region. In the superconducting state, ${1/T}_{1}$ has no Hebel-Slichter coherence peak just below ${T}_{C}$ and a power-law T dependence (close to ${T}^{3})$ at very low temperatures, which indicates the existence of line nodes in the superconducting energy gap. The ${}^{115}\mathrm{In}$ (Ce-In plane) Knight shift in ${\mathrm{CeCoIn}}_{5}$ decreases for both parallel and perpendicular directions to the tetragonal c axis in the superconducting state, which shows that the spin susceptibility decreases in all directions. These results indicate that ${\mathrm{CeCoIn}}_{5}$ and ${\mathrm{CeIrIn}}_{5}$ exhibit non-$s$-wave even parity (probably d-wave) superconductivity.