Effect of impurity scattering on superconductivity in K${}_2$Cr${}_3$As${}_3$

Impurity scattering in a superconductor may serve as an important probe for the nature of superconducting pairing state. Here we report the impurity effect on superconducting transition temperature $T_{\mathrm{c}}$ in the newly discovered Cr-based superconductor K${}_2$Cr${}_3$As${}_3$. The resistivity measurements show that the crystals prepared using high-purity Cr metal ($\ge$99.99%) have an electron mean free path much larger than the superconducting coherence length. For the crystals prepared using impure Cr that contains various \emph{nonmagnetic} impurities, however, the $T_{\mathrm{c}}$ decreases significantly, in accordance with the generalized Abrikosov-Gor’kov pair-breaking theory. This finding supports a non-$s$-wave superconductivity in K${}_2$Cr${}_3$As${}_3$.