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

Abstract

The in-plane resistivity ρ and thermal conductivity κ of the FeAs-based superconductor KFe2As2 single crystal were measured down to 50 mK. We observe non-Fermi-liquid behavior ρ(T)∼T1.5 at Hc2=5T, and the development of a Fermi liquid state with ρ(T)∼T2 when further increasing the field. This suggests a field-induced quantum critical point, occurring at the superconducting upper critical field Hc2. In zero field, there is a large residual linear term κ0/T, and the field dependence of κ0/T mimics that in d-wave cuprate superconductors. This indicates that the superconducting gaps in KFe2As2 have nodes, likely d-wave symmetry. Such a nodal superconductivity is attributed to the antiferromagnetic spin fluctuations near the quantum critical point. © 2010 The American Physical Society.