Abstract
We have studied optical transmission spectra of exfoliated α-RuCl3 flakes as a function of thickness and strain. While we do not find intrinsic changes of the electronic structure as a function of thickness down to d ≈ 3 nm, a uniaxial strain dependence of the principal gap excitation and higher lying multiplet states is observed, which changes sign according to its compressive or tensile character. In particular, the gap decreases under tensile strain and the intensity ratio of the gap excitation, which is due to a d4 triplet final state, with respect to the singlets at higher energy increases significantly. The d4 triplet is involved in the superexchange interaction between neighboring Ru sites and is, therefore, sensitive to nearest-neighbor spin-spin correlations. The experimental observations indicate an enhancement of the Kitaev interactions relative to competing interactions like the Heisenberg exchange J under tensile strain.
Acknowledgements
We thank A. Isaeva and M. Roslova for crystal preparation and characterization. This work has been supported by the German Research Foundation (DFG) under SFB 1143, project-id 247310070. AK acknowledges support by DFG grant KO...