Physics-Uspekhi, vol.65, no.7, pp.740-747, 2022 (SCI-Expanded, Scopus)
In the new stoichiometric high-temperature iron-based superconductor RbEuFe4As4, superconductivity coexists with a peculiar long-range magnetic order of the Eu 4f states; their coexistence is an enigma and a challenge for both experi-ment and theory. Using angle-resolved photoemission spectro-scopy (ARPES), resonant photoemission spectroscopy (ResPES), Andreev reflection spectroscopy, scanning tunnel-ing spectroscopy, and DFT band structure calculations, we have made significant progress in solving this puzzle. Our results unambiguously indicate a separation between the electronic states of Fe (superconductivity) and Eu (magnetism) and de-monstrate the existence of superconducting and long-range magnetic orders almost independently of each other.