Penetration depth study of LaOs$_4$Sb$_{12}$: Multiband s-wave superconductivity

TL;DR

This study investigates the magnetic penetration depth in LaOs$_4$Sb$_{12}$ single crystals, revealing multiband s-wave superconductivity with a smaller-than-BCS gap and unusual superfluid density behavior.

Contribution

First detailed measurement of penetration depth in LaOs$_4$Sb$_{12}$ showing multiband s-wave superconductivity with a reduced gap value.

Findings

Exponential temperature dependence indicating s-wave gap

Zero temperature gap Δ(0) smaller than BCS prediction

Superfluid density suggests two-band superconductivity

Abstract

We measured the magnetic penetration depth $\lambda(T)$ in single crystals of LaOs$_{4}$Sb$_{12}$ ($T_c$=0.74 K) down to 85 mK using a tunnel diode oscillator technique. The observed low-temperature exponential dependence indicates a s-wave gap. Fitting the low temperature data to BCS s-wave expression gives the zero temperature gap value $\Delta (0)= (1.34 \pm 0.07) k_B T_c$ which is significantly smaller than the BCS value of 1.76$k_B T_c$. In addition, the normalized superfluid density $\rho(T)$ shows an unusually long suppression near $T_c$, and are best fit by a two-band s-wave model.