Anomalous Fermi-Surface Dependent Pairing in a Self-Doped High-Tc Superconductor

TL;DR

This paper reports the discovery of a self-doped high-Tc superconductor with distinct superconducting gaps on different Fermi surface sheets, challenging existing theories on pairing mechanisms in cuprates.

Contribution

It introduces a new self-doped multi-layer superconductor with unconventional Fermi surface-dependent pairing properties.

Findings

Different superconducting gaps on two Fermi surface sheets.

The larger gap is on the electron-doped Fermi surface.

The electron-doped sheet has a shape disfavoring traditional pairing features.

Abstract

We report the discovery of a self-doped multi-layer high Tc superconductor Ba2Ca3Cu4O8F2(F0234) which contains distinctly different superconducting gap magnitudes along its two Fermi surface(FS) sheets. While formal valence counting would imply this material to be an undoped insulator, it is a self-doped superconductor with a Tc of 60K, possessing simultaneously both electron- and hole-doped FS sheets. Intriguingly, the FS sheet characterized by the much larger gap is the electron-doped one, which has a shape disfavoring two electronic features considered to be important for the pairing mechanism: the van Hove singularity and the antiferromagnetic (Pi/a, Pi/a) scattering.