Superconductivity in Fe-Based Compound EuAFe4As4 (A = Rb and Cs)

We report the discovery of a novel Fe-based superconductor EuAFe(4)As(4) (A = Rb, Cs) and describe its superconducting properties. EuAFe(4)As(4) has a tetragonal unit cell with a P4/mmm (No. 123) space group, indicating that this material is an 1144-type compound. The magnetic susceptibility and electrical resistivity indicate superconducting transitions at approximately 36 and 35K for EuRbFe4As4 and EuCsFe4As4, respectively. Moreover, an anomalous magnetic transition appears at approximately 15 K, suggesting the coexistence of superconductivity and a magnetic ordered state formed by the Eu2+ ions. The determined upper critical magnetic fields and coherence lengths are approximately 920 kOe and 1.8 nm for EuRbFe4As4 and 875 kOe and 1.9 nm for EuCsFe4As4, respectively.