Multiband superconductivity in V3Si determined from studying the response to controlled disorder

The London penetration depth, λ(T), was measured in a single crystal V₃Si. The superfluid density obtained from this measurement shows a distinct signature of two almost decoupled superconducting gaps. This alone is insufficient to distinguish between s_± and s₊₊ pairing states, but it can be achieved by studying the effect of a controlled non-magnetic disorder on the superconducting transition temperature, T_c. For this purpose, the same V₃Si crystal was sequentially irradiated by 2.5 MeV electrons three times, repeating the measurement between the irradiation runs. A total dose of 10 C/cm² (6.24 × 10¹⁹ electrons/cm² ) was accumulated, for which T_c has changed from 16.4 K in a pristine state to 14.7 K (9.3 %). This substantial suppression is impossible for a single isotropic gap, but also it is not large enough for a sign-changing s± pairing state. Our electronic band-structure calculations show how five bands crossing the Fermi energy can be naturally grouped to support two effective gaps, not dissimilar from the iron pnictides physics. We analyze the results using two-gap models for both, λ(T) and T_c, which describe the data very well. Finally, the experimental results and theoretical analysis provide strong support for an s₊₊ superconductivity with two unequal gaps, Δ₁ (0) ≈ 2.53 meV and Δ₂ (0) ≈ 1.42 meV, and a very weak inter-band coupling in V₃Si superconductor.