Quasi-2D Fermi surface of superconducting line-nodal metal CaSb$_2$

Abstract

We report on the Fermi surfaces and superconducting parameters of CaSb$_2$ single crystals (superconducting below $T_{\text{c}}\sim 1.8~\text{K}$) grown by the self-flux method. The frequency of de-Haas-van-Alphen and Shubnikov-de-Haas oscillations evidences a quasi-two-dimensional (quasi-2D) Fermi surface, consistent with one of the Fermi surfaces forming Dirac lines predicted by first-principles calculations. Measurements in the superconducting state reveal that CaSb$_2$ is close to a type-I superconductor with the Ginzburg-Landau (GL) parameter of around unity. The temperature dependence of the upper critical field $H_{\text{c2}}$ is well described by a model considering two superconducting bands, and the enhancement of the effective mass estimated from $H_{\text{c2}}(0~\text{K})$ is consistent with the quasi-2D band observed by the quantum oscillations. Our results indicate that a quasi-2D band forming Dirac lines contributes to the superconductivity in CaSb$_2$.