Homecond-mat.str-elarXiv:2605.30293

Spectroscopic evidence for a molecular orbital Kondo insulator

cond-mat.str-elcond-mat.mtrl-sci2026-05v1license

Abstract

A Kondo insulator (KI) is a prototypical example of a highly entangled phase of matter, where many-body interactions between local moments and delocalized electrons engender the non-magnetic insulating ground state. Conventionally, the local moments arise from atomic multiplet states with a narrow bandwidth, limiting Kondo coherence to low temperatures. Here, we realize a new paradigm for constructing the KI state with hybridized molecular orbitals in FeSb2. Resonant inelastic X-ray scattering (RIXS) at the Fe L-edge reveals distinct signatures of band-like continuum states and localized states. Comparisons with first-principles calculations establish a mixed-configuration ground state with hybridized Fe d-Sb p molecular orbitals as basis states. By systematically investigating the RIXS momentum, temperature, and doping dependences, we find propagating collective modes commensurate with many-body charge and spin excitations. Our results pave the way for understanding the emerging class of unconventional d electron insulators and engineering high temperature Kondo many-body states.

Cite

@article{arxiv.2605.30293,
  title  = {Spectroscopic evidence for a molecular orbital Kondo insulator},
  author = {Ke-Jun Xu and Kuan H. Hsu and Nathan Giles-Donovan and Christopher T. Parzyck and Gi-Hyeok Lee and Wanli Yang and Jun Okamoto and Hsiao-Yu Huang and Di-Jing Huang and Joshua J. Kas and John Vinson and Zhi-Xun Shen and Dung-Hai Lee and Thomas P. Devereaux and Wei-Sheng Lee and Robert J. Birgeneau},
  journal= {arXiv preprint arXiv:2605.30293},
  year   = {2026}
}