Muon spin relaxation measurements of magnetic-field penetration depth in Ba8Si46

Muon spin relaxation (mu SR) and high-field magnetization measurements have been performed in Ba8S46, a superconductor with T-c = 8 K having a silicon clathrate three-dimensional cage structure. The upper critical field H-c2 = 6.5 T, determined from the magnetization, indicates a short coherence length xi = 72 Angstrom. The magnetic field penetration depth lambda(T --> 0) = 4000 Angstrom was obtained from the muon spin relaxation rate sigma(T --> 0) similar to 0.46 mu s(-1) observed in transverse fields of 0.1-1 T. These values of xi and lambda indicate that this system is a strongly type-II superconductor with a high value of kappa = 56, We deduce the effective Fermi temperature T-F and compare the present system with other superconducting systems in a plot of T-c versus T-F. (C) 2000 Elsevier Science B.V. All rights reserved.