Microscopic nature of phase I in CeRh2As2

Establish the microscopic nature of phase I, the ordered state of the Ce-4f moments that develops below T0 = 0.55 K in CeRh2As2, including whether it is antiferromagnetic, multipolar, or itinerant in origin.

Background

CeRh2As2 exhibits an ordered phase of the Ce-4f moments below T0 = 0.55 K, followed by superconductivity below Tc = 0.35 K. Although a spontaneous internal field has been detected, suggesting antiferromagnetism, the enhancement of T0 by an in-plane magnetic field and the emergence of additional field-induced phases challenge a simple antiferromagnetic interpretation.

The paper discusses competing explanations involving dipolar and higher-multipolar order in a local crystal-electric-field framework, as well as an itinerant scenario driven by Fermi-surface nesting. Determining the microscopic order is important for clarifying its relationship to unconventional superconductivity and the multiple superconducting phases.

References

The microscopic nature of phase I has not been fully established yet.

— La substitution studies on the heavy-fermion superconductor CeRh$_2$As$_2$  (2609.17080 - Sankar et al., 15 Sep 2026) in Abstract; Section Introduction

While the interplay of phase I with superconductivity can be reasonably understood within a Ginzburg--Landau description, the microscopic origin and nature of this order remain unclear.

— Multiorbital periodic Anderson model for CeRh2As2  (2609.31001 - Hackner et al., 25 Sep 2026) in Section 1, Introduction