  The electronic structure of the topmost layer in Sr2RuO4 in the close
vicinity of the Fermi level is investigated by angle-resolved photoemission
spectroscopy (ARPES) with a 7-eV laser. We find that the spin-orbit coupling
(SOC) predicted as 100 meV by the density functional theory (DFT) calculations
is enormously enhanced in a real material up to 250 meV, even more than that of
bulk state (200 meV), by the electron-correlation effect increased by the
octahedral rotation in the crystal structure. This causes the formation of
highly orbital-mixing small Fermi pockets and reasonably explains why the
orbital-selective Mott transition (OSMT) is not realized in perovskite oxides
with crystal distortion. Interestingly, Hund's metal feature allows the
quasiparticle generation only near EF, restricting the spectral gap opening
derived by band hybridization within an extremely small binding energy (< 10
meV). Furthermore, it causes coherent-incoherent crossover, making the Fermi
pockets disappear at elevated temperatures. The anomalous Fermi pockets are
characterized by the dichotomy of the orbital-isolating Hund's coupling and the
orbital-mixing SOC, which is key to understanding the nature of Sr2RuO4.
