Investigation of phonon anharmonicity in Ca2RuO4

Ca2RuO4, a sister compound of the well-known unconventional superconductor Sr2RuO4, has been the subject of intense research interest due to the variety of exotic phenomena it exhibits such as current-induced non-equilibrium states, soft Higgs mode, anomalous negative thermal expansion etc. Our recent diffuse x-ray scattering experiments revealed a giant phonon softening in extended regions of the Brillouin zone, which implies large lattice anharmonicity effects that has not been previously reported in this material. Here we propose to perform non-resonant inelastic x-ray scattering measurements on single crystals of Ca2RuO4 to further investigate the phonon dynamics. We expect that our experiments will enable a deeper understanding of the lattice anharmonicity and anomalous structural properties of the system and possibly also help understand the giant lattice softening that was recently observed near the uniaxial strain induced Liftshitz transition in Sr2RuO4.