Anomalous Fermi pockets on Hund's metal surface of Sr2RuO4 induced by the correlation-enhanced spin-orbit coupling

TL;DR

This study reveals that correlation effects significantly enhance spin-orbit coupling in Sr2RuO4, leading to anomalous Fermi pockets and unique electronic behavior influenced by Hund's metal characteristics and crystal structure distortions.

Contribution

It demonstrates the correlation-induced enhancement of spin-orbit coupling and its impact on Fermi surface topology in Sr2RuO4, providing new insights into Hund's metal behavior and orbital mixing effects.

Findings

Spin-orbit coupling is enhanced from 100 meV to 250 meV due to electron correlations.

Formation of small, orbital-mixed Fermi pockets explained by enhanced SOC.

Fermi pockets disappear at higher temperatures due to Hund's metal effects.

Abstract

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.