Research Highlight

A first-principles approach to identifying nontrivial order in the rare-earth compound CeRh₂As₂

A rare-earth compound discovered in 2021,

CeRh₂As₂, is known as a “multiphase superconductor” that exhibits multiple superconducting states under magnetic fields. In addition, it displays a rich variety of physical properties in which multiple orders coexist and compete, including the coexistence of superconductivity and antiferromagnetism, as well as the emergence of a nontrivial ordered phase (called Phase I) above the superconducting transition temperature. While conventional antiferromagnetic order is generally suppressed and destroyed by external magnetic fields, Phase I of CeRh₂As₂ exhibits a characteristic anisotropy in which the order is enhanced only under in-plane magnetic fields. At present, active debate continues regarding whether the origin of Phase I is magnetic order or electric quadrupole order, as well as its relationship to multiphase superconductivity and antiferromagnetism.

To identify the order parameter of Phase I in CeRh₂As₂, we performed first-principles calculations of quantities known as “multipole fluctuations” using the DFT+DMFT method, which combines density functional theory (DFT) with dynamical mean-field theory (DMFT). Our calculations revealed the development of antiferromagnetic fluctuations and clarified that Phase I corresponds to a two-dimensional antiferromagnetic order characterized by magnetic moments aligned along the c-axis. Furthermore, we demonstrated that the enhancement of the order under in-plane magnetic fields can be explained by contributions from field-induced electric quadrupoles.

This study represents one of the few successful examples in which a first-principles approach has been applied not only to reproduce known ordered states but also to elucidate nontrivial hidden ordered states in rare-earth compounds. The fact that the proposed ordered state is consistent with experimental observations demonstrates that this method is a powerful approach for uncovering unknown properties of strongly correlated materials.

K. Numa, E. Matsuda, A. Kirikoshi, J. Otsuki
Phys. Rev. B 113, 115141 (2026) – Published 18 March, 2026