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Free keywords:
Europium compounds, Iron compounds, Iron-based Superconductors, Magnetic fields, Magnetic moments, Photoelectron spectroscopy, Rubidium compounds, Superconducting magnets, Temperature distribution, Topology, Angle resolved photoemission spectroscopy, Electrical resistances, External magnetic field, Magnetic superconductors, Pulsed magnetic fields, Superconducting state, Temperature dependence, Topological transitions, Electron spin resonance spectroscopy
Abstract:
We study single crystals of the magnetic superconductor EuRbFe4As4 by magnetization, electron spin resonance (ESR), angle-resolved photoemission spectroscopy, and electrical resistance in pulsed magnetic fields up to 63 T. The superconducting state below 36.5 K is almost isotropic and is only weakly affected by the development of Eu2+ magnetic order at 15 K. On the other hand, for the external magnetic field applied along the c axis the temperature dependence of the ESR linewidth reveals a Berezinskii-Kosterlitz-Thouless topological transition below 15 K. This indicates that Eu2+ planes are a good realization of a two-dimensional XY magnet, which reflects the decoupling of the Eu2+ magnetic moments from superconducting FeAs layers. © 2021 American Physical Society.