Abstract

The unconventional superconductor CeRh2As2 hosts two distinct superconducting states at ambient pressure, which earned the material a significant attention [1]. In line with the established paradigm of unconventional superconductivity, the system also hosts another ordered state, setting in at the critical temperature T0 = 0.55 K [2]. While recent experiments clearly point at an antiferromagnetic order parameter, a concomitant multipolar ordering of higher order than a dipole is necessary in order to explain the strong enhancement of T0 observed when a magnetic field is applied along the basal plane of the tetragonal lattice.
In this talk, we give an overview of the unusual T0 order of CeRh2As2. We show how the crystal-electric-field scheme of the Ce ion enables multipolar degrees of freedom and interpret the field-temperature phase diagram of the compound through the lens of the model of coupled magnetic and quadrupolar order [3]. We also present our recent data on the magnetic basal-plane anisotropy of T0, further supporting the existence of higher-order multipolar ordering in CeRh2As2 [4].
1. S. Khim & J. Landaeta et al., Science 373, 1012–1016 (2021).
2. P. Khanenko et al., Phys. Rev. B 112, L060501 (2025).
3. B. Schmidt & P. Thalmeier, Phys. Rev. B 110, 075154 (2024).
4. K. Semeniuk et al. arXiv: 2601.10414 (2026).