Evidence for short-range antiferromagnetic fluctuations in Kondo-insulating YbB12

TL;DR

This study reveals short-range antiferromagnetic fluctuations in the Kondo-insulating compound YbB12 through inelastic neutron scattering, showing a spin gap and dispersive excitations consistent with a spin exciton in a hybridization gap system.

Contribution

It provides direct experimental evidence of short-range antiferromagnetic correlations in YbB12, linking spin excitations to the hybridization gap in Kondo insulators.

Findings

Detection of a spin gap with two sharp in-gap excitations.

The lower excitation is linked to short-range antiferromagnetic correlations.

Results align with the spin exciton model in hybridization gap semiconductors.

Abstract

The spin dynamics of mixed-valence YbB12 has been studied by inelastic neutron scattering on a high-quality single crystal. In the Kondo-insulating regime realized at low temperature, the spectra exhibit a spin-gap structure with two sharp, dispersive, in-gap excitations at E = 14.5 and approximately 20 meV. The lower mode is shown to be associated with short-range correlations near the antiferromagnetic wave vector q0 = (1/2, 1/2, 1/2). Its properties are in overall agreement with those expected for a "spin exciton'' branch in an indirect hybridization gap semiconductor.