We report an x-ray photoemission spectroscopy study of Ca2RuO4 surface-dosed with Cs alkali atoms and C60 molecules. Due to its small ionization energy (large electron affinity), deposited Cs atoms (C60 molecules) are expected to provide a solid surface with electrons (holes). Upon dosing the dopants to Mott-insulating Ca2RuO4, we found a new Ru 3d photoemission peak emerging on the lower binding-energy side, suggesting the creation of a core-hole screening channel associated with coherent Ru 4d states around the Fermi level. For both the Cs and C60 dosing, this change occurred without an appreciable chemical potential jump. The coherent state, therefore, develops within the Mott gap through hybridization with the impurity level of the dopants. The present work highlights the flexibility of Mott-insulator surfaces as a playground for metal-insulator transitions.
@article{arxiv.2602.15610,
title = {Ambipolar doping-induced surface in-gap state on Mott-insulating Ca$_2$RuO$_4$},
author = {M. Horio and T. Wada and V. Granata and R. Fittipaldi and A. Vecchione and J. Chang and I. Matsuda},
journal= {arXiv preprint arXiv:2602.15610},
year = {2026}
}