Phonon-tunable THz magnonic emission in multiferroic heterostructures

TL;DR

This paper demonstrates tunable, narrowband terahertz emission in multiferroic heterostructures by coupling phonons, magnons, and strain waves, advancing THz source technology.

Contribution

It introduces a method to generate tunable THz emission via phonon-magnon coupling in multiferroic heterostructures at room temperature.

Findings

Efficient sub-bandgap optical rectification near 2 THz in BiFeO3 films.

Tunable narrowband THz emission between 0.4-0.8 THz in Pt/BiFeO3 bilayers.

Coupling of electromagnons with strain waves enables control of THz emission.

Abstract

Collective excitations such as magnons and polar phonons provide natural access to the terahertz (THz) regime, but efficient generation and tunability remain elusive. Multiferroic BiFeO3 combines both orders at room temperature, offering a unique platform for narrowband THz emission. Here, we achieve efficient sub-bandgap optical rectification of coupled phonon-polaritons near 2 THz in bare epitaxial thin films. In Pt/BiFeO3 bilayers, we demonstrate that coupling the electromagnon branch with ultrafast strain waves, optically generated in Pt layers with various thicknesses, can produce tunable and narrowband emission between 0.4-0.8 THz. These results uncover the intertwined role of phonons, magnons, and magneto-acoustic dynamics in antiferromagnetic multiferroics, and establish these hybrid platforms as versatile engineered narrowband THz sources.