139La NQR relaxation in superconductor LaRu3Si2

LaRu 3 Si 2 reveals superconductivity below the superconducting transition temperature T c ∼6.5 K, which is important concerning with a valence fluctuating material CeRu 3 Si 2 with T c ∼1K, in which 4f spins are considered to depress its superconducting transition. The magnetic susceptibility of LaRu 3 Si 2 is very dependent on temperature, which indicates a narrow band of conduction electrons. To investigate the relation between the superconducting state and 4f spin fluctuations, 139 La NQR relaxation rate 1/T 1 has been measured in LaRu 3 Si 2 without 4f spins. In the normal state, 1/T 1 is proportional to temperature. The superconductivity in LaRu 3 Si 2 is found to be BCS type because 1/T 1 shows a coherence peak just below T c and an Arrhenius type dependence exp(-2Δ/k B T) well below T c .