Antiferromagnetic dichroism and Davydov splitting of 3d-excitons in a complex multisublattice magnetoelectric CuB2O4

TL;DR

This study reveals large antiferromagnetic linear dichroism in CuB2O4 linked to magnetic Davydov splitting of 3d-excitons, uncovering a novel magnetic phase transition and complex spiral magnetic structure.

Contribution

It demonstrates the microscopic origin of dichroism in CuB2O4 and introduces a spectroscopic method to detect hidden magnetic features and phase transitions.

Findings

Large antiferromagnetic linear dichroism observed

Microscopic link to magnetic Davydov splitting established

Identification of a novel magnetic phase transition and elliptical spiral structure

Abstract

The space and time symmetry breaking at magnetic phase transitions in multiferroics results in a number of strongly pronounced optical effects. Our high-resolution spectroscopic study of 3d- excitons in a complex multi-sublattice magnetoelectric CuB2O4 demonstrates that, among those, a large antiferromagnetic linear dichroism is observed which is highly sublattice-sensitive to subtle changes in the spin subsystems. We prove that the discovered linear dichroism is related microscopically to the magnetic Davydov splitting of the exciton states. We announce a novel magnetic phase transition and argue that an elliptical spiral structure rather than a simple circular helix is realized in the incommensurate phase, these findings being overlooked in previous studies by optical and other techniques. We claim that this spectroscopic method can be effectively applied to other materials for revealing hidden features of magnetic structures and phase transitions.