Orbital-Dependent Band Narrowing Revealed in an Extremely Correlated Hund's Metal Emerging on the Topmost Layer of Sr2RuO4

摘要

We use a surface-selective angle-resolved photoemission spectroscopy and unveil the electronic nature on the topmost layer of Sr2RuO4 crystal, consisting of slightly rotated RuO6 octahedrons. The. band derived from the 4d(xy) orbital is found to be about three times narrower than that for the bulk. This strongly contrasts with a subtle variation seen in the a and a bands derived from the one-dimensional 4d(xz/yz). This anomaly is reproduced by the dynamical mean-field theory calculations, introducing not only the onsite Hubbard interaction but also the significant Hund's coupling. We detect a coherence-to-incoherence crossover theoretically predicted for Hund's metals, which has been recognized only recently. The crossover temperature in the surface is about half that of the bulk, indicating that the naturally generated monolayer of reconstructed Sr2RuO4 is extremely correlated and well isolated from the underlying crystal.