Dynamic Spin-Lattice Coupling and Statistical Interpretation for the Molecular-Like Excitations in Frustrated Pyrochlores

Emergent molecular-like excitations have been discovered in a series of pyrochlore antiferromagnets, yet their origins and relationships with the coexisting magnon excitations remain a puzzle. Here, by incorporating the dynamic spin-lattice coupling through the site-phonon model, we accomplish a unified description of the molecular and magnon excitations, which allows us to provide a statistical interpretation of the molecular-like modes. Our work also demonstrates a semiclassical approach to understand exotic spin dynamics in systems with non-bilinear spin interactions.