Coexistence of local magnetism and superconductivity in the heavy-fermion CeRh$_2$As$_2$ revealed by $\mu$SR studies

TL;DR

This study uses muon spin relaxation to reveal that in CeRh$_2$As$_2$, local magnetism coexists with superconductivity below 0.55 K, suggesting a complex ordered state involving Ce-4$f$ moments.

Contribution

It provides direct evidence of magnetic order and its coexistence with superconductivity in CeRh$_2$As$_2$, clarifying the nature of the $T_o$ phase and its relation to Ce-4$f$ moments.

Findings

Magnetic order appears below 0.55 K.

Microscopic coexistence of magnetism and superconductivity.

The $T_o$ phase involves Ce-4$f$ moments.

Abstract

The superconducting (SC) state ($T_\mathrm{c}$ = 0.3 K) of the heavy-fermion compound CeRh$_2$As$_2$, which undergoes an unusual field-induced transition to another high-field SC state, emerges from an unknown ordered state below $T_\mathrm{o}$ = 0.55 K. While an electronic multipolar order of itinerant Ce-4$f$ states was proposed to account for the $T_\mathrm{o}$ phase, the exact order parameter has not been known to date. Here, we report on muon spin relaxation ($\mu$SR) studies of the magnetic and SC properties in CeRh$_2$As$_2$ single crystals at low temperatures. We reveal a magnetic origin of the $T_\mathrm{o}$ order by identifying a spontaneous internal field below $T_\mathrm{o}$ = 0.55 K. Furthermore, we find evidence of a microscopic coexistence of local magnetism with bulk superconductivity. Our findings open the possibility that the $T_\mathrm{o}$ phase involves both dipole and higher order Ce-4$f$ moment degrees of freedom and accounts for the unusual non-Fermi liquid behavior.