Superconducting energy gap structure of CsVSbfrom magnetic penetration depth measurements.

Experimental determination of the structure of the superconducting order parameter in the kagome lattice compound CsVSbis an essential step towards understanding the nature of the superconducting pairing in this material. Here we report measurements of the temperature dependence of the in-plane magnetic penetration depth,λ(T), in crystals of CsVSbdown to∼60mK. We find thatλ(T)is consistent with a fully-gapped state but with significant gap anisotropy. The magnitude of the gap minima are in the range∼0.2-0.3 Tcfor the measured samples, markedly smaller than previous estimates. We discuss different forms of potential anisotropy and how these can be linked to the V and Sb Fermi surface sheets. We highlight a significant discrepancy between the calculated and measured values ofλ(T=0)which we suggest is caused by spatially suppressed superconductivity.