Phase diagram and weak-link behavior in Nd-doped CaFe2As2

Bo Gao,Ang Li,Qiucheng Ji,Gang Mu,Wei Li,Xiaoming Xie,Xiaojiang Li,Tao Hu

doi:10.1088/1367-2630/16/11/113024

Abstract

The transport properties, phase diagram, and dopant distribution are investigated in systematically Nd-doped CaFe2As2 single crystals. Coexistence of two superconducting (SC) phases with different critical transition temperature (Tc) is observed. The low-Tc phase emerges as x ≥ 0.031, and the Tc value increases to its maximum value of about 20 K at x = 0.083, the maximum doping level in our study. As x ≥ 0.060, the high-Tc phase with a Tc value of about 40 K is observed. The structure transition (STr) from tetragonal to orthorhombic phase vanishes suddenly around x = 0.060, where a new STr from tetragonal to collapsed tetragonal phase begins to turn up. Compared to the low-Tc phase, the end point of SC transition of the high-Tc phase is more sensitive to the magnetic field, showing a characteristic of Josephson weak-link behavior. Possible scenarios about this system are discussed based on our observations. We also find that the non-uniform SC properties cannot be attributed to the heterogeneous Nd distribution on the micro scale, as revealed by the detailed energy dispersive x-ray spectroscopy measurements.

Highlights

Fe-based superconductors have been studied extensively since the report ofLaFeAsO1-xFx with Tc of 26 K [1, 2]
The AFe2As2 compounds (A=Ba, Sr, Ca, Eu, so called “122” system) with the ThCr2Si2-type structure [3] are widely studied because single crystals with high quality are accessible [4]
We report a systematic investigation of the characterization and phase diagram of the electron-doped Ca1-xNdxFe2As2 single crystals

Summary

Introduction

Fe-based superconductors have been studied extensively since the report ofLaFeAsO1-xFx with Tc of 26 K [1, 2]. Electron-doping usually induces superconductivity at a lower temperature (around 22 K) by substituting Fe ions with other transition metals [7,8,9]. We report a systematic investigation of the characterization and phase diagram of the electron-doped Ca1-xNdxFe2As2 single crystals. The behaviors of field induced resistance broadening for superconducting transition are observed, indicating a weak-link feature in the present system.

Results

Conclusion