Angular dependence of the upper critical field in CaAlSi single crystal: Deviation from the Ginzburg-Landau anisotropic mass model

Abstract

The anisotropic upper critical field in CaAlSi with an ${\mathrm{AlB}}_{2}$ structure has been investigated by magnetic, transport, and specific heat measurements. The variation of ${H}_{c2}$ with $\ensuremath{\theta},$ the angle between the $\mathrm{ab}$ plane and the applied field, determined from the transport measurements at various temperatures, show a cusplike behavior near $\ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{}$ unlike the prediction of the Ginzburg-Landau anisotropic mass model. Rather, the angular dependence is consistent with Tinkham's formula for thin film superconductors. We have found an increase in the anisotropy parameter with temperature. The negligible in-plane anisotropy of ${H}_{c2}$ is consistent with the small mean free path in this compound.