Transport properties, upper critical field and anisotropy of Ba(Fe$_{0.75}$Ru$_{0.25}$)$_2$As$_2$ single crystals

TL;DR

This study investigates the anisotropic superconducting properties of Ba(Fe$_{0.75}$Ru$_{0.25}$)$_2$As$_2$ single crystals, revealing an anisotropy ratio similar to other doped Ba122 compounds, and suggests the Fermi surface warping is not significantly affected by Ru doping.

Contribution

The paper provides the first detailed measurement of the anisotropy and upper critical field slopes in Ru-doped Ba122, comparing it with other doped variants to understand Fermi surface effects.

Findings

Anisotropy ratio approximately 2 in Ba(Fe$_{0.75}$Ru$_{0.25}$)$_2$As$_2$

Similar anisotropy to K- and Co-doped Ba122 compounds

Fermi surface warping in Ru-doped samples is not significantly different

Abstract

The temperature and angle dependent resistivity of Ba(Fe$_{0.75}$Ru$_{0.25}$)$_2$As$_2$ single crystals were measured in magnetic fields up to 14 T. The temperature dependent resistivity with the magnetic field aligned parallel to c-axis and ab-planes allow us to derive the slope of d$H_{c2}^{ab}/dT$ and d$H_{c2}^c/dT$ near $T_c$ yielding an anisotropy ratio $\Gamma=dH_{c2}^{ab}/dT/dH_{c2}^c/dT \approx$ 2. By scaling the curves of resistivity vs. angle measured at a fixed temperature but different magnetic fields within the framework of the anisotropic Ginzburg-Landau theory, we obtained the anisotropy in an alternative way. Again we found that the anisotropy $(m_c/m_{ab})^{1/2}$ was close to 2. This value is very similar to that in Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ (K-doped Ba122) and Ba(Fe$_{0.92}$Co$_{0.08}$)$_2$As$_2$ (Co-doped Ba122). This suggests that the 3D warping effect of the Fermi surface in Ru-doped samples may not be stronger than that in the K-doped or Co-doped Ba122 samples, therefore the possible nodes appearing in Ru-doped samples cannot be ascribed to the 3D warping effect of the Fermi surface.