Pressure evolution of the normal- and superconducting-state properties of the line-nodal material ${\mathrm{CaSb}}_2$ revealed by ${}_{123}\mathrm{Sb}$ nuclear quadrupole resonance

${\mathrm{CaSb}}_2$ 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 $T_c$ 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. $T_c$ 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 $N\left(E_F\right)$, which is one of the parameters governing $T_c$, is insensitive to pressure. From these results, we conclude that $N\left(E_F\right)$ does not govern the origin of the enhancement in $T_c$. 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.