We report an investigation of the superconducting order parameter of the noncentrosymmetric compound ${\mathrm{PbTaSe}}_2$, which is believed to have a topologically nontrivial band structure. Precise measurements of the London penetration depth $\mathrm{\Delta }\lambda \left(T\right)$ obtained using a tunnel diode oscillator (TDO) based method show an exponential temperature dependence at $T\ll T_c$, suggesting a nodeless superconducting gap structure. A single-gap $s$-wave model well describes the corresponding normalized superfluid density ${\rho }_s\left(T\right)$, with a gap magnitude of $\mathrm{\Delta }\left(0\right)\simeq 1.88T_c$. This is very close to the value of $1.76T_c$ for weak-coupling BCS superconductors, indicating conventional fully-gapped superconductivity in ${\mathrm{PbTaSe}}_2$.

• Penetration depth
• Superconducting order parameter
• Superconductors
• BCS theory
• Tunnel diode resonance