Magnetic penetration depth in V3Si and LiTi2O4 measured by μSR

Muon spin relaxation (μSR) studies have been performed in the normal spinel LiTi2O4 and the A-15 superconductor V3Si to measure the magnetic penetration depth λ. The relaxation rateσ(T) ∝ 1/λ2 in field-cooled measurements shows a sharp increase belowTc followed by saturation at low temperatures in both systems. This feature implies an isotropic energy gap without anomalous zeros, and most likelys-wave pairing. The low temperature penetration depth λ(T → 0) is determined to be 2100Å for LiTi2O4 and 1300Å for V3Si respectively. Assuming a clean limit relationσ ∝ λ−2 ∝ns/m*, we derive the Fermi temperatureTF ∝ns/2/3m* from the relaxation rateσ and the Sommerfeld constantγ asTF ∝ σ3/4γ−1/4. Unlike conventional superconductors, both LiTi2O4 and V3Si have a large ratio ofTc/TF ≈ 0.01, only slightly smaller than those ratios in more exotic superconductors.