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Title: Competing Electronic Ground States in the Heavy-Fermion Superconductor CeRh₂As₂

Authors: J. Bławat, G. Chajewski, D. Gnida, J. Singleton, O. Ayala Valenzuela, D. Kaczorowski, R. D. McDonald

Journal: Physical Review X

DOI: 10.1103/m44c-tzrj

The article demonstrates that in the heavy-fermion superconductor CeRh₂As₂, a magnetic field can “switch” the system between different electronic ground states depending on the field orientation. When the field is applied along the c axis, a pronounced change in the electronic properties occurs at around 24 T: the concentration of charge carriers increases sharply, with holes remaining the dominant carriers. Transport measurements and Hall-effect data indicate that this behavior is associated with a reconstruction of the electronic structure, most likely caused by a weakening of the Kondo effect and partial localization of the f electrons. In this sense, a strong magnetic field reduces the contribution of f electrons to electrical transport, which may correspond to a field-induced valence transition or a closely related phenomenon.
In contrast, when the magnetic field lies in the ab plane of the crystal, a sequence of new field-induced phases emerges. These phases are characterized by a pronounced anisotropy of the electrical conductivity, reflecting its dependence on the direction of the applied current, and by dome-shaped phase boundaries in the temperature–field phase diagrams. The absence of significant anomalies in magnetization suggests that these transitions are not of conventional magnetic origin but instead correspond to density-wave–type phases. This implies that in CeRh₂As₂ the magnetic field not only modifies superconducting properties but also promotes the formation of alternative electronically ordered states. As a result, this material provides an excellent model system for studying the competition between superconductivity and other forms of electronic order in strongly correlated electron systems.