Coexistence of Magnetism and Superconductivity in the Iron-based Compound Cs_0.8(FeSe_0.98)_2

TL;DR

This study demonstrates the microscopic coexistence of magnetism and superconductivity in Cs_0.8(FeSe_0.98)_2, with magnetic order persisting well above the superconducting transition temperature, revealing a unique interplay in this iron-based compound.

Contribution

It provides the first detailed evidence of microscopic coexistence of magnetism and superconductivity in Cs_0.8(FeSe_0.98)_2 using multiple measurement techniques.

Findings

Superconductivity occurs below T_c = 28.5 K.

Magnetic order exists below T_N = 478.5 K.

The magnetic and superconducting phases coexist microscopically.

Abstract

We report on muon-spin rotation/relaxation (\muSR), electrical resistivity, magnetization and differential scanning calorimetry measurements performed on a high-quality single crystal of Cs_0.8(FeSe_0.98)_2. Whereas our transport and magnetization data confirm the bulk character of the superconducting state below T_c = 28.5(2)K, the \muSR data indicate that the system is {\it magnetic} below T_N = 478.5(3)K, where a first-order transition occurs. The first-order character of the magnetic transition is confirmed by differential scanning calorimetry data. Taken all together, these data indicate in Cs_0.8(FeSe_0.98)_2 a microscopic coexistence between the superconducting phase and a strong magnetic phase. The observed ratio between T_N and T_c is the highest one reported to date for a magnetic superconductor.