• Abdel-Hafiez, M.; Johansson, F. O. L.; Chakraborty, A.; Pavelka, M.; Ghosh, A.; Chareev, D. A.; Vasiliev, A. N.; Edström, A.; Delin, A.; Eriksson, O.; Karmakar, D.; Phuyal, D.: Charge-transfer properties and electron dynamics in ferromagnetic CoS2. Physical Review B 112 (2025), p. 165115/1-10

10.1103/vg4c-h785
Open Accesn Version

Abstract:
We investigated the element-specific electronic structure and charge-carrier dynamics of a single-crystal ferromagnet CoS2 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 CoS2 that is compared against the isoelectronic paramagnet CoSe2 . The Co 1⁢𝑠 core-level line shows several satellite features for CoS2 , showing explicit charge-transfer processes and local screening of the core hole by S ligands, whereas no such features are observed in CoSe2 . The satellite structures indicate the electronic configuration of divalent Co2+ as a combination of 𝑑8⁢Ḻ and 𝑑9⁢Ḻ2 in addition to the nominal ionic 𝑑7 state, where Ḻ represents an S 3⁢𝑝 hole. We employ resonant Auger spectroscopy across the S 𝐾 -edge for CoS2 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 3⁢𝑑 and S 3⁢𝑝 states with pronounced charge-transfer character reflects a self-doped system with a finite density 𝑛 of holes at the sulfur site (Ḻ𝑛 ), in line with recent models that indicate a negative charge-transfer energy for CoS2 . 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 CoS2 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 CoS2 with a wide potential in topological spintronics applications and integration in energy-related device platforms.