Terahertz Spin Dynamics in Dirac Antiferromagnet CoTiO3
Rolando Valdes Aguilar
Department of Physics, Ohio State University
Abstract.– Recently the study of the interplay between topology and magnetism has started to gain attention. A few materials have been identified to host topologically non-trivial magnons, while many more theoretical proposals continue to be made. One recent example of a potential topological magnetic material is CoTiO3, which purportedly hosts Dirac magnons. We use a combination of time domain THz (TDTS) and magneto-Raman spectroscopies to measure the low energy magnetic spectrum in CoTiO3 and detect the two lowest energy modes, one of which is the unexpectedly gapped Goldstone mode. We propose a mechanism for the opening of this gap by invoking the presence of the ring-exchange interaction between spins in a single hexagonal plaquette. The addition of this exchange to the Hamiltonian is able to explain most of the features of experiments, including the mangetic field dependence of the magnon frequencies. This study shows the power of combining TDTS and Raman spectroscopies to understand the nature of the magnetic excitations in quantum magnets.