${\mathrm{CaSb}}_2$ is the Dirac line-nodal material that exhibits a superconducting (SC) transition at 1.7 K. In spite of its conventional SC state at ambient pressure, the transition temperature $T_{\mathrm{c}}$ shows a peak structure against hydrostatic pressure. We performed ac magnetic susceptibility and ${}^{123}\mathrm{Sb}$ nuclear quadrupole resonance (NQR) measurements on single-crystalline ${\mathrm{CaSb}}_2$ under pressures up to 2.08 GPa. $T_{\mathrm{c}}$ monotonically increased in this pressure region, which is consistent with a previous study. We observed continuous broadening of the NQR spectrum against pressure, which is a sign of unique compression behavior of the lattice. In the normal state, the nuclear spin-lattice relaxation rate $1/T_1$ is proportional to temperature in all pressure values, typical of a metal. However, $1/T_{1}T$ in the normal state is independent of pressure, indicating that the density of states at the Fermi energy $N\left(E_{\mathrm{F}}\right)$, which is one of the parameters governing $T_{\mathrm{c}}$, is insensitive to pressure. From these results, we conclude that $N\left(E_{\mathrm{F}}\right)$ does not govern the origin of the enhancement in $T_{\mathrm{c}}$. This is unusual for a weak electron-phonon coupling superconductor. In the SC state, we revealed that the SC gap becomes larger and more isotropic under pressure.

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• Superconductivity
• Superconductors
• Topological materials
• Nuclear quadrupole resonance
• Pressure techniques