Disorder by Design in Quantum Materials

Compositionally complex materials represent a paradigm shift in quantum materials design, where controlled chemical disorder enables diverse magnetic and electronic microstates to emerge from ordered crystalline lattices. We present recent results on high entropy oxides that demonstrate novel approaches to manipulating cation charge state degeneracy. By controlling the variance of accessible spin, charge, and orbital parameters across different cation sites, we observe dramatic charge redistribution mediated by nearest-neighbor interactions. Through X-ray absorption spectroscopy and resonant inelastic X-ray scattering, we reveal a complex interplay between local and extended electronic states, where certain sites maintain rigid charge states while others exhibit metallic-like electron delocalization despite bulk insulating behavior. This apparent contradiction suggests the emergence of a charge glass state driven by configurational entropy, analogous to spin glasses in frustrated magnets. Our findings demonstrate how engineered disorder and degeneracy can unlock unexpected electronic and magnetic properties, opening new pathways to explore fundamental questions in quantum many-body physics while enabling functionalities for next-generation technologies.