Quantum criticality and nodal superconductivity in the FeAs-based superconductor KFe2As2

Abstract

The in-plane resistivity $\rho$ and thermal conductivity $\kappa$ of FeAs-based superconductor KFe${}_2$As${}_2$ single crystal were measured down to 50 mK. We observe non-Fermi-liquid behavior $\rho (T)\sim T^{1.5}$ at $H_{c_2}$ = 5 T, and the development of a Fermi liquid state with $\rho (T)\sim T^2$ when further increasing 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 ${\kappa }_0/T$, and the field dependence of ${\kappa }_0/T$ mimics that in d-wave cuprate superconductors. This indicates that the superconducting gaps in KFe${}_2$As${}_2$ have nodes, likely d-wave symmetry. Such a nodal superconductivity is attributed to the antiferromagnetic spin fluctuations near the quantum critical point.

4 pages, 4 figures - replaces arXiv:0909.4855

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