La-NQR Probe of Strong-Coupling s-Wave Superconductivity in LaRu₃Si₂

Abstract

To investigate the electronic state of LaRu₃Si₂, we have carried out ¹³⁹La-NQR measurement. In the normal state, the spin–lattice relaxation rate 1⁄T₁ is proportional to the temperature T. 1⁄T₁ shows a coherence peak just below the superconducting transition temperature T_c=6.5 K and decreases exponentially well below T_c. LaRu₃Si₂ is found to be a strong coupling BCS superconductor with a large energy gap 2Δ(0)=5.50k_BT_c. A relatively high T_c in LaRu₃Si₂ is presumably due to a high density of states of conduction electrons at Fermi surface and strong electron–phonon interaction.