Resonant magnetic exciton mode in the heavy-fermion antiferromagnet CeB6

TL;DR

This paper reports the discovery of a resonant magnetic exciton mode in the heavy-fermion antiferromagnet CeB6, revealing similarities to modes in unconventional superconductors and suggesting a role of itinerant spin dynamics and hidden order parameters.

Contribution

It introduces the observation of a non-dispersive resonant mode in CeB6 linked to a hidden antiferro-quadrupolar order, expanding understanding of magnetic excitations in correlated-electron systems.

Findings

Resonant mode is non-dispersive and concentrated at a specific wave vector.

Mode energy increases below the antiferromagnetic transition temperature.

The mode shares characteristics with resonant modes in unconventional superconductors.

Abstract

Resonant magnetic excitations are widely recognized as hallmarks of unconventional superconductivity in copper oxides, iron pnictides, and heavy-fermion compounds. Numerous model calculations have related these modes to the microscopic properties of the pair wave function, but the mechanisms underlying their formation are still debated. Here we report the discovery of a similar resonant mode in the non-superconducting, antiferromagnetically ordered heavy-fermion metal CeB6. Unlike conventional magnons, the mode is non-dispersive, and its intensity is sharply concentrated around a wave vector separate from those characterizing the antiferromagnetic order. The magnetic intensity distribution rather suggests that the mode is associated with a coexisting order parameter of the unusual antiferro-quadrupolar phase of CeB6, which has long remained "hidden" to the neutron-scattering probes. The mode energy increases continuously below the onset temperature for antiferromagnetism, in parallel to the opening of a nearly isotropic spin gap throughout the Brillouin zone. These attributes bear strong similarity to those of the resonant modes observed in unconventional superconductors below their critical temperatures. This unexpected commonality between the two disparate ground states indicates the dominance of itinerant spin dynamics in the ordered low-temperature phases of CeB6 and throws new light on the interplay between antiferromagnetism, superconductivity, and "hidden" order parameters in correlated-electron materials.