THz Magneto-electric atomic rotations in the chiral compound Ba$_3$NbFe$_3$Si$_2$O$_{14}$

TL;DR

This study investigates the terahertz spectrum of the chiral compound Ba$_3$NbFe$_3$Si$_2$O$_{14}$, revealing magnetic and magnetoelectric excitations linked to atomic rotations and helical polarization.

Contribution

It provides the first terahertz spectral analysis of this chiral langasite, identifying distinct magnetic and magnetoelectric excitations and their underlying atomic mechanisms.

Findings

Identification of a magnon in the magnetically ordered phase.

Detection of a magnetoelectric excitation persisting into the paramagnetic phase.

Observation of atomic rotations associated with helical electric polarization.

Abstract

We have determined the terahertz spectrum of the chiral langasite Ba$_3$NbFe$_3$Si$_2$O$_{14}$ by means of synchrotron-radiation measurements. Two excitations are revealed that are shown to have a different nature. The first one, purely magnetic, is observed at low temperature in the magnetically ordered phase and is assigned to a magnon. The second one persits far into the paramagnetic phase and exhibits both an electric and a magnetic activity at slightly different energies. This magnetoelectric excitation is interpreted in terms of atomic rotations and requires a helical electric polarization.