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

TL;DR

This study investigates the quantum critical behavior and nodal superconductivity in KFe2As2, revealing a field-induced quantum critical point and d-wave-like nodal gaps through resistivity and thermal conductivity measurements.

Contribution

It provides experimental evidence of quantum criticality and nodal superconductivity in KFe2As2, highlighting the role of antiferromagnetic fluctuations.

Findings

Non-Fermi-liquid resistivity at Hc2=5 T

Fermi liquid behavior at higher fields

Nodal superconducting gaps with d-wave symmetry

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.