Superconducting electronic state in optimally doped YBa2Cu3O7-d observed with laser-excited angle-resolved photoemission spectroscopy

TL;DR

This study uses laser-excited ARPES to investigate the electronic structure of optimally doped YBa2Cu3O7-d, revealing a clear bulk superconducting state, significant bilayer splitting, and a nonzero minimum gap suggesting unconventional superconductivity.

Contribution

First laser-excited ARPES study to observe the bulk superconducting state in YBa2Cu3O7-d, providing detailed insights into its electronic structure and gap behavior.

Findings

Bulk superconducting state observed without surface state interference

Bilayer splitting of ~0.08 Å^{-1} along (0,0)-(π,π)

Superconducting gap shows d_{x^2-y^2} symmetry with a nonzero minimum of ~12 meV

Abstract

Low energy electronic structure of optimally doped YBa2Cu3O7-d is investigated using laser-excited angle-resolved photoemission spectroscopy. The surface state and the CuO chain band that usually overlap the CuO2 plane derived bands are not detected, thus enabling a clear observation of the bulk superconducting state. The observed bilayer splitting of the Fermi surface is ~0.08 angstrom^{-1} along the (0,0)-(pi,pi) direction, significantly larger than Bi2Sr2CaCu2O8+d. The kink structure of the band dispersion reflecting the renormalization effect at ~60 meV shows up similarly as in other hole-doped cuprates. The momentum-dependence of the superconducting gap shows d_{x^2-y^2}-wave like amplitude, but exhibits a nonzero minimum of ~12 meV along the (0,0)-(pi,pi) direction. Possible origins of such an unexpected "nodeless" gap behavior are discussed.