Different resistivity response to spin density wave and superconductivity at 20 K in $Ca_{1-x}Na_xFe_2As_2$

TL;DR

This study investigates the anisotropic resistivity and magnetic properties of CaFe2As2, revealing distinct responses to spin-density-wave ordering and superconductivity, with Na doping suppressing SDW and inducing superconductivity around 20 K.

Contribution

It provides detailed measurements of resistivity anisotropy and magnetic behavior, highlighting the contrasting resistivity responses to SDW and superconductivity in Ca1-xNaxFe2As2.

Findings

Resistivity anisotropy is approximately 50, less than in BaFe2As2.

SDW ordering causes a steep resistivity increase in CaFe2As2.

Na doping suppresses SDW and induces superconductivity at ~20 K.

Abstract

We report that intrinsic transport and magnetic properties, and their anisotropy from high quality single crystal $CaFe_2As_2$. The resistivity anisotropy ($\rho_c/\rho_{ab}$) is $\sim 50 $, and less than 150 of $BaFe_2As_2$, which arises from the strong coupling along c-axis due to an apparent contraction of about 0.13 nm compared to $BaFe_2As_2$. Temperature independent anisotropy indicates that the transport in ab plane and along c-axis direction shares the same scattering mechanism. In sharp contrast to the case of parent compounds $ROFeAs$ (R=rare earth) and $MFe_2As_2$ (M=Ba and Sr), spin-density-wave (SDW) ordering (or structural transition) leads to a steep increase of resistivity in $CaFe_2As_2$. Such different resistivity response to SDW ordering is helpful to understand the role played by SDW ordering in Fe-based high-$T_c$ superconductors. The susceptibility behavior is very similar to that observed in single crystal $BaFe_2As_2$. A linear temperature dependent susceptibility occurs above SDW transition of about 165 K. Partial substitution of Na for Ca suppresses the SWD ordering (anomaly in resistivity) and induces occurrence of superconductivity at $\sim 20$ K.