Type: Article
Publication Date: 2010-02-26
Citations: 223
DOI: https://doi.org/10.1103/physrevlett.104.087005
The in-plane resistivity $\ensuremath{\rho}$ and thermal conductivity $\ensuremath{\kappa}$ of the FeAs-based superconductor ${\mathrm{KFe}}_{2}{\mathrm{As}}_{2}$ single crystal were measured down to 50 mK. We observe non-Fermi-liquid behavior $\ensuremath{\rho}(T)\ensuremath{\sim}{T}^{1.5}$ at ${H}_{{c}_{2}}=5\text{ }\text{ }\mathrm{T}$, and the development of a Fermi liquid state with $\ensuremath{\rho}(T)\ensuremath{\sim}{T}^{2}$ when further increasing the field. This suggests a field-induced quantum critical point, occurring at the superconducting upper critical field ${H}_{{c}_{2}}$. In zero field, there is a large residual linear term ${\ensuremath{\kappa}}_{0}/T$, and the field dependence of ${\ensuremath{\kappa}}_{0}/T$ mimics that in $d$-wave cuprate superconductors. This indicates that the superconducting gaps in ${\mathrm{KFe}}_{2}{\mathrm{As}}_{2}$ have nodes, likely $d$-wave symmetry. Such a nodal superconductivity is attributed to the antiferromagnetic spin fluctuations near the quantum critical point.