NMR and NQR studies of the heavy fermion superconductors $\mathrm{Ce}T{\mathrm{In}}_5\hspace{0.5em}(T=\mathrm{Co}$ and Ir)

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.