Spin-ordering Mediated Orbital Hybridization in CoO at High Pressures

We demonstrate a strong dependence of high-resolution 1s3p (or K-beta) resonant x-ray emission spectroscopy (RXES) on local spin correlations at high pressure. We show that the pre-edge region in K-beta RXES of CoO can be separated into a local quadrupolar contribution and nonlocal dipolar intensity, which arises from the mixing of cobalt 4p states with neighboring cobalt 3d orbitals. For pressures of 0-12 GPa, we observe a twofold increase in nonlocal contributions with respect to local contributions. For pressures greater than 12 GPa, the ratio remains nearly constant. The observed pressure dependence and strong intensity changes cannot be explained by a conventional picture of bond-length shortening and is ascribed to increased intersite 4p-3d mixing due to changes in magnetic ordering. These results are supported by theoretical calculations.