Coexistence of metallicity and superconductivity in adjacent bilayers of a high-Tc superconductor

TL;DR

This study reveals that YBCO's ARPES spectra contain two components from different bilayers, showing a large superconducting gap and anisotropic renormalization, thus advancing understanding of high-Tc superconductivity in cuprates.

Contribution

It demonstrates that YBCO's ARPES spectrum includes two distinct bilayer contributions, resolving a long-standing puzzle and supporting the universality of superconducting properties across cuprates.

Findings

Identification of two components in YBCO ARPES spectra.

Observation of a large superconducting gap in the bulk component.

Evidence of anisotropic renormalization in YBCO.

Abstract

Experimental studies of the electronic structure remain the basic means for understanding the nature of high-temperature superconductivity (HTSC) and testing relevant theoretical models. Appreciable contributions to establish the overall picture in HTSC have recently been made by investigations on the charge dynamics in BSCCO (ref. 1) and the spin dynamics in YBCO, using Angle Resolved Photoemission Spectroscopy (ARPES) and Inelastic Neutron Scattering (INS), respectively. Concentration of each of these techniques on a "suitable" compound turns out to be a barrier on the way to a crucial quantitative test allowing to support or discard spin fluctuations (interaction between the charge and spin degrees of freedom) as a possible origin for the pairing in doped cuprates. Here we solve the long-standing puzzle of ARPES on YBCO by showing that the photoelectron spectrum of YBCO generally includes two components: One from the topmost anomalously overdoped metallic CuO2 bilayer and the other from the next superconducting bilayer that retains the bulk properties. Our findings clearly show the opening of a large superconducting gap and, for the first time, demonstrate the anisotropic renormalization in the bulk component of YBCO, supporting the universality of these effects for different cuprate families. With our study we re-open this cuprate family for new systematic ARPES investigations.