Bulk and surface low-energy excitations in YBa2Cu3O7-d studied by high-resolution angle-resolved photoemission spectroscopy

TL;DR

This study uses high-resolution ARPES to clarify the electronic structure of YBa2Cu3O7-delta, revealing surface and bulk band behaviors and their relation to superconductivity, resolving longstanding controversies in high-Tc cuprates.

Contribution

The paper provides the first clear identification of surface and bulk bands in YBa2Cu3O7-delta and their distinct electronic properties, especially regarding the superconducting gap and electron-boson interactions.

Findings

Surface bands are highly overdoped with no gap or anomaly.

Bulk bands exhibit a dx2-y2-wave superconducting gap.

Bulk quasiparticles show strong electron-boson coupling.

Abstract

We have performed high-resolution angle-resolved photoemission spectroscopy on YBa2Cu3O7-delta (Y123; delta = 0.06; Tc = 92 K). By accurately determining the Fermi surface and energy band dispersion, we solve long-standing controversial issues as to the anomalous electronic states of Y-based high-Tc cuprates. We unambiguously identified surface-bilayer-derived bonding and antibonding bands, together with their bulk counterparts. The surface bands are highly overdoped (hole concentration x = 0.29), showing no evidence for the gap opening or the dispersion anomaly in the antinodal region, while the bulk bands show a clear dx2-y2-wave superconducting gap and the Bogoliubov quasiparticle-like behavior with a characteristic energy scale of 50-60 meV indicative of a strong electron-boson coupling in the superconducting state. All these results suggest that the metallic and superconducting states coexist at the adjacent bilayer of Y123 surface.