Penetration Depth Study Of Laos4sb12: Multiband S-Wave Superconductivity

We measured the magnetic penetration depth lambda(T) in single crystals of LaOs4Sb12 (T-c = 0.74 K) down to 85 mK using a tunnel-diode-oscillator technique. The observed low-temperature exponential dependence indicates an s-wave gap. Fitting the low-temperature data to a BCS s-wave expression gives the zero-temperature gap value Delta(0) = (1.34 +/- 0.07)k(B)T(c) which is significantly smaller than the BCS value of 1.76k(B)T(c). In addition, the normalized superfluid density rho(T) shows an unusually long suppression near T-c and is best fit by a two-band s-wave model.