Nodeless superconductivity in noncentrosymmetric PbTaSe${}_2$ single crystals

We report an investigation of the superconducting order parameter of the noncentrosymmetric compound PbTaSe${}_2$, which is believed to have a topologically nontrivial band structure. Precise measurements of the London penetration depth $\mathrm{\Delta }\lambda (T)$ 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 band s-wave model well describes the corresponding normalized superfluid density, with a gap magnitude of $\mathrm{\Delta }(0)=1.85T_c$. This is very close to the value of $1.76T_c$ for weak-coupling BCS superconductors, indicating conventional fully-gapped superconductivity in PbTaSe${}_2$.