Fully gapped superconductivity without sign reversal in the topological superconductor PbTaSe2

We investigate the superconducting gap function of the topological superconductor ${\mathrm{PbTaSe}}₂$. The temperature, magnetic field, and three-dimensional (3D) field-angle dependences of the specific heat prove that the superconductivity of ${\mathrm{PbTaSe}}₂$ is fully gapped, with two isotropic $s$-wave gaps. The pair-breaking effect is probed by systematically increasing nonmagnetic disorders through ${\mathrm{H}}⁺$ irradiation. The superconducting transition temperature ${T}_{\mathrm{c}}$ is found to be robust against disorders, which suggests that the pairing should be sign preserved rather than sign reversed.