Insights from ARPES for an undoped, four-layered, two-gap high-T_c superconductor

TL;DR

This study uses ARPES to analyze an undoped four-layer cuprate superconductor, revealing how electronic correlations and structural features influence its Fermi surface and superconducting gaps, highlighting the role of reduced screening and interlayer interactions.

Contribution

It provides new insights into the electronic structure and pairing mechanisms of a four-layered high-T_c superconductor, emphasizing the effects of correlations and layer-specific charge dynamics.

Findings

Fermi surface features include large n- and p-doped sheets with different SC gaps.

Electronic correlations reduce screening and affect interlayer charge transfer.

Localization of n-sheets on inner layers protects d-wave pairing from impurities.

Abstract

An undoped cuprate with apical fluorine and inner (i) and outer (o) CuO2-layers is a 60 K superconductor whose Fermi surface (FS) has large n- and p-doped sheets with the SC gap on the n-sheet twice that on the p -sheet (Y. Chen et al.). The Fermi surface is not reproduced by the LDA, but the screening must be substantially reduced due to electronic correlations, and oxygen in the o-layers must be allowed to dimple outwards. This charges the i-layers by 0.01|e|, causes an 0.4 eV Madelung-potential difference between the i and o -layers, quenches the i-o hopping, and localizes the n-sheets onto the i-layers, thus protecting their d-wave pairs from being broken by scattering on impurities in the BaF layers. The correlation-reduced screening strengthens the coupling to z-axis phonons.