Low temperature enhancement of ferromagnetic Kitaev correlations in {\alpha}-RuCl3

TL;DR

This study uses electron energy loss spectroscopy to demonstrate that ferromagnetic Kitaev interactions in lpha-RuCl3 are enhanced at low temperatures, confirming the ferromagnetic nature of these correlations through spectral weight analysis.

Contribution

It provides direct spectroscopic evidence supporting ferromagnetic Kitaev interactions in lpha-RuCl3, aligning experimental data with theoretical models.

Findings

Spectral weight of triplet excitations increases at low temperature.

Temperature dependence matches ferromagnetic Kitaev coupling predictions.

EELS spectral weight correlates with Kitaev-type spin correlations.

Abstract

Kitaev-type interactions between neighbouring magnetic moments emerge in the honeycomb material ${\alpha}$-RuCl3. It is debated however whether these Kitaev interactions are ferromagnetic or antiferromagnetic. With electron energy loss spectroscopy (EELS) we study the lowest excitation across the Mott-Hubbard gap, which involves a d4 triplet in the final state and therefore is sensitive to nearest-neighbor spin-spin correlations. At low temperature the spectral weight of these triplets is strongly enhanced, in accordance with optical data. We show that the magnetic correlation function that determines this EELS spectral weight is directly related to a Kitaev-type spin-spin correlator and that the temperature dependence agrees very well with the results of a microscopic magnetic Hamiltonian for ${\alpha}$-RuCl3 with ferromagnetic Kitaev coupling.