Magnon-phonon coupling in a Dirac magnet CoTiO₃

Magnon-phonon coupling has been an intense research topic due to its numerous applications in spintronics and magnonics. Recently, cobalt titanate (CoTiO₃), an easy-plane quantum antiferromagnet, has been found to host topological magnons and has been predicted to have a relatively large phonon magnetic moment. We have investigated the effect of coherent chiral phonons on the magnetic properties of CoTiO₃ using terahertz pump-optical Faraday rotation probe spectroscopy. Our results showed phonon-driven excitation of the antiferromagnetic magnon mode and a gradual increase in the Faraday as a function of pump-probe delay time with no measurable decay. We found that the observed THz-induced rotation was highly temperature dependent, and thus, we conclude that it is related to the magnetic order in this material. We will discuss the possible origins of the observed phenomena.