Charge-transfer properties and electron dynamics in ferromagnetic CoS 2

We investigated the element-specific electronic structure and charge-carrier dynamics of a single-crystal ferromagnet {CoS}₂ with complementary x-ray spectroscopy techniques. Hard x-ray photoemission (HAXPES) is used to provide crucial information on the bulk electronic structure and chemical bonding in {CoS}₂ that is compared against the isoelectronic paramagnet {CoSe}₂ . The Co 1s core-level line shows several satellite features for {CoS}₂ , showing explicit charge-transfer processes and local screening of the core hole by S ligands, whereas no such features are observed in {CoSe}₂ . The satellite structures indicate the electronic configuration of divalent {Co}²⁺ as a combination of {d}⁸Ḻ and {d}⁹{Ḻ}² in addition to the nominal ionic {d}⁷ state, where Ḻ represents an S 3p hole. We employ resonant Auger spectroscopy across the S K -edge for {CoS}₂ to obtain electron delocalization times to adjacent Co atomic sites. The fast carrier dynamics are attributed to strongly screened Coulomb interactions and hence a facile carrier delocalization. The strong hybridization formed between the Co 3d and S 3p states with pronounced charge-transfer character reflects a self-doped system with a finite density n of holes at the sulfur site ( {Ḻ}ⁿ ), in line with recent models that indicate a negative charge-transfer energy for {CoS}₂ . In addition to HAXPES data, we also report on experimental and theoretical L -edge x-ray absorption and x-ray magnetic circular dichroism data for {CoS}₂ that demonstrate multiconfiguration effects in the excitation process. To enable a direct comparison of the experimental spectra, we used density functional theory calculations to obtain the projected density of states to describe the ground-state electronic structure. The existence of fast carrier dynamics and strong charge-transfer properties, demonstrated in this study, highlights the unique nature of {CoS}₂ with a wide potential in topological spintronics applications and integration in energy-related device platforms.