Observation of Robust In-gap Edge States in EuRbFe₄As₄

The study of in-gap excitations in a superconductor is vital for understanding its pairing symmetry and exploring Majorana boundary modes. Here, we report pronounced in-gap edge states in the iron-based superconductor EuRbFe₄As₄ using scanning tunneling microscopy and spectroscopy. These edge states appear at full-unit-cell and half-unit-cell steps, with a consistent spatial decay length of approximately 1.8 nm. Systematic temperature-dependent measurements show that the edge states persist above the magnetic transition temperature yet vanish upon exiting the superconducting state, linking them to superconducting pairing rather than ferromagnetism. Furthermore, the absence of interaction between adjacent edge states indicates their chiral nature. Our findings position EuRbFe₄As₄ as a platform for unconventional superconductivity and functional devices.