Theory of electromagnon in the multiferroic Mn perovskites: Vital role of higher harmonic components of the spiral spin order

TL;DR

This paper provides a theoretical analysis of electromagnons in multiferroic Mn perovskites, emphasizing the importance of higher harmonic components in the spiral spin order for understanding optical spectra and magnon modes.

Contribution

It introduces a realistic spin Hamiltonian that accounts for higher harmonics, explaining experimental double-peak spectra and predicting magnon branches for neutron scattering tests.

Findings

Double-peak optical spectrum explained by hybridized magnon modes.

Higher harmonic components are crucial for accurate modeling.

Predicted magnon branches can be experimentally verified.

Abstract

We study theoretically the electromagnon and its optical spectrum (OS) of the terahertz-frequency regime in the magnetic-spiral-induced multiferroic phases of the rare-earth (R) Mn perovskites, RMnO3, taking into account the elliptical deformation or the higher harmonics of the spiral spin configuration, which has been missed so far. A realistic spin Hamiltonian, which gives phase diagrams in agreement with experiments, resolves a long standing puzzle, i.e., the double-peak structure of the OS with a larger low-energy peak originating from magnon modes hybridized with the zone-edge state. We also predict the magnon branches associated with the electromagnon, which can be tested by neutron-scattering experiment.