Evidence of Strong Orbital-Selective Spin-Orbital-Phonon Coupling in ${\mathrm{CrVO}}_4$

Coupling of orbital degree of freedom with a spin exchange, i.e., Kugel-Khomskii-type interaction (KK), governs a host of material properties, including colossal magnetoresistance, enhanced magnetoelectric response, and photoinduced high-temperature magnetism. In general, KK-type interactions lead to deviation in experimental observables of coupled Hamiltonian near or below the magnetic transition. Using diffraction and spectroscopy experiments, here we report anomalous changes in lattice parameters, electronic states, spin dynamics, and phonons at four times the Néel transition temperature ($T_N$) in ${\mathrm{CrVO}}_4$. The temperature is significantly higher than other $d$-orbital compounds such as manganites and vanadates, where effects are limited to near or below $T_N$. The experimental observations are rationalized using first-principles and Green's function-based phonon and spin simulations that show unprecedentedly strong KK-type interactions via a superexchange process and an orbital-selective spin-phonon coupling coefficient at least double the magnitude previously reported for strongly coupled spin-phonon systems. Our results present an opportunity to explore the effect of KK-type interactions and spin-phonon coupling well above $T_N$ and possibly bring various properties closer to application, for example, strong room-temperature magnetoelectric coupling.