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

TL;DR

This study investigates the Fermi surface and superconducting properties of CaSb$_2$, revealing a quasi-2D Fermi surface with Dirac lines and multi-band superconductivity, suggesting a link between the electronic structure and superconducting behavior.

Contribution

It provides the first experimental evidence of a quasi-2D Fermi surface with Dirac lines in CaSb$_2$ and analyzes its superconducting parameters with a multi-band model.

Findings

Quasi-2D Fermi surface confirmed by quantum oscillations.

CaSb$_2$ exhibits multi-band superconductivity.

Superconductivity is close to type-I with a GL parameter around unity.

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$_2$.