Electronic specific heat in BaFe$_{2-x}$Ni$_x$As$_2$

TL;DR

This study investigates the low-temperature electronic specific heat in BaFe$_{2-x}$Ni$_x$As$_2$ single crystals across the superconducting dome, revealing nonlinear behavior and the influence of spin fluctuations on electronic states.

Contribution

It introduces a model incorporating ferromagnetic spin fluctuations to explain the nonlinear temperature dependence of electronic specific heat in doped BaFe$_{2-x}$Ni$_x$As$_2$.

Findings

Normal-state electronic specific heats may be nonlinear with temperature.

Ferromagnetic spin fluctuations can explain specific heat data.

Fermi-surface topology influences electronic states.

Abstract

We have systematically studied the low-temperature specific heat of the BaFe$_{2-x}$Ni$_x$As$_2$ single crystals covering the whole superconducting dome. Using the nonsuperconducting heavily overdoped x = 0.3 sample as a reference for the phonon contribution to the specific heat, we find that the normal-state electronic specific heats in the superconducting samples may have a nonlinear temperature dependence, which challenges previous results in the electron-doped Ba-122 iron-based superconductors. A model based on the presence of ferromagnetic spin fluctuations may explain the data between x = 0.1 and x = 0.15, suggesting the important role of Fermi-surface topology in understanding the normal-state electronic states.