Temperature dependent superfluid density in Ta-Doped CsV₃Sb₅ determined by small-angle neutron scattering measurements of the vortex lattice

We have used small-angle neutron scattering to study the vortex lattice (VL) in Cs(V_0.86Ta_0.14)₃Sb₅ as a function of temperature. For this Ta-doping, the Charge Density Wave (CDW) observed in the 135 family of kagome superconductors is suppressed below T_c. The VL was prepared by field cooling to base temperature in applied fields of 0.1 T and 0.2 T, followed by a dampled field oscillation. Measurements were then performed as the sample is heated from 70 mT to T_c. At all measured fields and temperatures the VL has a triangular symmetry with Bragg peaks aligned along the [-1 2 0] crystalline directions. No disordering of the VL is observed as the temperature is increased. From measurements of the scattered intensity we determine the temeperature-dependent superfluid density, which follows that expected for an s-wave superconductor. However, at T ≈ 250 mK the scattered intensity exhibits a jump which may be due to the formation of a CDW phase.