Optical phonon dynamics in Kitaev spin liquid candidate materials

In our study, we employ optical phonon dynamics to investigate the fractionalization of spin degrees of freedom in the promising Kitaev spin liquid candidate materials, namely α-RuCl₃ (a 2D honeycomb lattice) and β-Li₂IrO₃ (a 3D hyperhoneycomb lattice). In particular we suggest that the signatures of spin fractionalization can be detected through a detailed analysis of the temperature and magnetic field dependencies of the asymmetric Fano lineshape of low-energy Raman-active optical phonons. Our study shows that both α-RuCl₃ and β-Li₂IrO₃ exhibit temperature-dependent Fano lineshapes that align with the fractionalization of spins into Majorana fermions and Z2 fluxes. These findings support the idea that these materials are in close proximity to the 2D and 3D Kitaev spin liquid phases respectively.