Low temperature specific heat of the hole-doped Ba_{0.6}K_{0.4}Fe_2As_2 single crystals and electron-doped SmFeAsO_{0.9}F_{0.1} samples

TL;DR

This study compares the low-temperature specific heat of hole-doped Ba_{0.6}K_{0.4}Fe_2As_2 and electron-doped SmFeAsO_{0.9}F_{0.1} superconductors, revealing significant differences in quasiparticle density of states and superconducting gap structures.

Contribution

It provides detailed specific heat measurements showing the multigap nature and high quasiparticle density of states in Ba_{0.6}K_{0.4}Fe_2As_2, highlighting differences from F-doped LnFeAsO systems.

Findings

High SH anomaly in Ba_{0.6}K_{0.4}Fe_2As_2 suggests high quasiparticle density of states.

Electronic SH coefficient indicates a dominant full superconducting gap in Ba_{0.6}K_{0.4}Fe_2As_2.

Multigap effects are evident from the inability to fit data with a single s-wave gap.

Abstract

Low temperature specific heat (SH) was measured on the FeAs-based superconducting single crystals Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ and high pressure synthesized polycrystalline samples SmFeAsO$_{0.9}$F$_{0.1}$. It is found that the sharp SH anomaly $\Delta C/T|_{T_c}$ in Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ reaches an unexpected high value of 98 mJ/mol K$^2$, about one order of magnitude larger than that of SmFeAsO$_{0.9}$F$_{0.1}$ ($6\sim8$ mJ/mol K$^2$) samples, suggesting very high normal state quasiparticle density of states in FeAs-122 than in FeAs-1111. Furthermore, we found that the electronic SH coefficient $\gamma_e(T)$ of Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ is weakly temperature dependent and increases almost linearly with the magnetic field in low temperature region, which may indicate that the hole-doped FeAs-122 system contains a dominant component with a full superconducting gap, although we cannot rule out the possibility of a small component with anisotropic or nodal gap. A detailed analysis reveals that the $\gamma_e(T)$ of Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ cannot be fitted with a single gap of s-wave symmetry probably due to the multigap effect. These results indicate clear difference between the properties of the superconducting state of the holed-doped Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ and the F-doped LnFeAsO (Ln = rare earth elements) systems, which we believe is originated from the complex Fermi surface structures in different systems.