Sinusoidal electromagnon in RMnO3: Indication of anomalous magnetoelectric coupling

TL;DR

This paper investigates the optical spectra of multiferroic RMnO3 manganites, revealing that anomalous magnetoelectric coupling explains the presence and behavior of electromagnons across different magnetic phases.

Contribution

It introduces the concept of anomalous magnetoelectric coupling breaking rotational invariance, explaining electromagnon phenomena in RMnO3.

Findings

Two strong electromagnons in the non-collinear phase

Only one electromagnon persists in the collinear phase

Anomalous magnetoelectric coupling causes oscillatory polarization

Abstract

The optical spectra in the family of multiferroic manganites RMnO3 is a great puzzle. Current models can not explain the fact that two strong electromagnons are present in the non-collinear spin cycloidal phase, with only one electromagnon surviving the transition into the collinear spin sinusoidal phase. We show that this is a signature of the presence of anomalous magnetoelectric coupling that breaks rotational invariance in spin space and generates oscillatory polarization in the ground state.