Comment on "Quantum Criticality and Nodal Superconductivity in the FeAs-Based Superconductor KFe$_2$As$_2$"

Abstract

In a recent Letter [J. K. Dong et al., Phys. Rev. Lett. 104, 087005 (2010)], Dong \textit{et al}. have observed a $T^{1.5}$ dependence of resistivity $ρ$ in KFe$_2$As$_2$ at the upper critical field $B_{c2}$ = 5 T parallel to the c axis and have suggested the existence of a field-induced quantum critical point (QCP) at $B_{c2}$. In this comment, we argue that observation of a $T^{1.5}$ dependence of $ρ$ in a sample showing broad resistive transitions does not constitute evidence for a QCP and that recent dHvA results do not support the proposed QCP.

3 pages, 2 figures + 1 supplemental figure, to be published in PRL