Muon Spin Relaxation Studies of Superconductivity in a Crystalline Array of Weakly Coupled Metal Nanoparticles

Abstract

We report Muon Spin Relaxation studies in weak transverse fields of the superconductivity in the metal cluster compound, Ga$\_84$[N(SiMe$\_3$)$\_2$]$\_20$-Li$\_6$Br$\_2$(thf)$\_20\cdot$2toluene. The temperature and field dependence of the muon spin relaxation rate and Knight shift clearly evidence type II bulk superconductivity below $T\_\text{c}\approx 7.8$ K, with $B\_\text{c1}\approx 0.06$ T, $B\_\text{c2}\approx 0.26$ T, $\kappa \sim 2$ and weak flux pinning. The data are well described by the s-wave BCS model with weak electron-phonon coupling in the clean limit. A qualitative explanation for the conduction mechanism in this novel type of narrow band superconductor is presented.

4 figures, 5 pages