In-situ electric field control of THz non-reciprocal directional dichroism in the multiferroic Ba$_2$CoGe$_2$O$_7$

TL;DR

This study demonstrates in-situ electric control of THz non-reciprocal directional dichroism in Ba$_2$CoGe$_2$O$_7$, enabling electric switching of magnetic domains and modulating non-reciprocal light absorption.

Contribution

It introduces a method for electric switching of magnetic domains in a multiferroic, controlling non-reciprocal THz light absorption in situ.

Findings

Electric switching of magnetic domains achieved in Ba$_2$CoGe$_2$O$_7$

Non-reciprocal THz light absorption modulated by domain population

Demonstration of electric control over magnetoelectric susceptibilities

Abstract

Non-reciprocal directional dichroism, also called the optical-diode effect, is an appealing functional property inherent to the large class of non-centrosymmetric magnets. However, the in-situ electric control of this phenomenon is challenging as it requires a set of conditions to be fulfilled: Special symmetries of the magnetic ground state, spin-excitations with comparable magnetic- and electric-dipole activity and switchable electric polarization. We demonstrate the isothermal electric switch between domains of Ba$_2$CoGe$_2$O$_7$ possessing opposite magnetoelectric susceptibilities. Combining THz spectroscopy and multiboson spin-wave analysis, we show that unbalancing the population of antiferromagnetic domains generates the non-reciprocal light absorption of spin excitations.