Electromagnon excitation in cupric oxide measured by Fabry-P\'erot enhanced terahertz Mueller matrix ellipsometry

TL;DR

This paper demonstrates a novel terahertz ellipsometry technique using Fabry-Pérot enhancement to detect electromagnon excitations in CuO, revealing detailed optical properties and temperature dependence with high sensitivity.

Contribution

The study introduces a Fabry-Pérot enhanced terahertz Mueller matrix ellipsometry method for detecting electromagnons in CuO, providing improved measurement sensitivity and detailed optical characterization.

Findings

Detected electromagnon peak at 0.705 THz and 215 K

Observed excitation along a specific polarizability axis

Results agree with previous THz-TDS measurements

Abstract

Here we present the use of Fabry-P\'erot enhanced terahertz (THz) Mueller matrix ellipsometry to measure an electromagnon excitation in monoclinic cupric oxide (CuO). As a magnetically induced ferroelectric multiferroic, CuO exhibits coupling between electric and magnetic order. This gives rise to special quasiparticle excitations at THz frequencies called electromagnons. In order to measure the electromagnons in CuO, we exploit single-crystal CuO as a THz Fabry-P\'erot cavity to resonantly enhance the excitation's signature. This enhancement technique enables the complex index of refraction to be extracted. We observe a peak in the absorption coefficient near 0.705 THz and 215 K, which corresponds to the electromagnon excitation. This absorption peak is observed along only one major polarizability axis in the monoclinic a-c plane. We show the excitation can be represented using the Lorentz oscillator model, and discuss how these Lorentz parameters evolve with temperature. Our findings are in excellent agreement with previous characterizations by THz time-domain spectroscopy (THz-TDS), which demonstrates the validity of this enhancement technique.