The kagome lattice naturally hosts flat bands, Dirac fermions, and van Hove singularities, yet whether its geometry can stabilize orbital-selective phases - a hallmark of Hund's physics in multi-orbital correlated systems - has remained an open question. Here, we combine resonant inelastic X-ray scattering with density functional theory and dynamical mean-field theory to demonstrate that YMn6Sn6 exhibits a spontaneous orbital differentiation into coexisting itinerant and localized electrons within the same Mn 3d manifold. Orbitals directed along Mn-Mn bonds provide coherent quasiparticles and metallic bands, while those pointing toward ligands become strongly correlated and display non-Fermi-liquid behavior. Hund's intra-atomic exchange suppresses orbital fluctuations, stabilizing this dichotomy and providing a natural double-exchange-like mechanism for the observed ferromagnetic bilayer coupling. Our work establishes YMn6Sn6 as a kagome platform where orbital selectivity, flat-band topology, and Hund's metallicity converge - revealing that geometric frustration and correlation-driven orbital differentiation can cooperatively design exotic quantum phases beyond the canonical paradigms of Mott physics or band topology alone.
@article{arxiv.2603.21203,
title = {Orbital-specific Itinerancy and Localization in a Kagome Magnet},
author = {S. V. Streltsov and H. Y. Huang and A. Ushakov and C. I. Wu and A. Singh and J. Su and J. Okamoto and C. T. Chen and K. Wang and A. I. Poteryaev and S-W. Cheong and A. Fujimori and D. J. Huang},
journal= {arXiv preprint arXiv:2603.21203},
year = {2026}
}