Anomalous asymmetry of the Fermi surface in the YBa2Cu4O8 high temperature superconductor revealed by Angle Resolved Photoemission Spectroscopy

TL;DR

This study reveals a significant in-plane asymmetry in the Fermi surface of YBa2Cu4O8 superconductor, caused by bilayer band splitting asymmetry, impacting the understanding of its superconducting and transport properties.

Contribution

It uncovers the anomalous in-plane asymmetry of the Fermi surface in YBa2Cu4O8 using ARPES, highlighting the role of bilayer band splitting asymmetry.

Findings

Strong in-plane asymmetry between a and b directions.

Higher energy saddle point in the antibonding band along a.

Opposite behavior in the bonding band.

Abstract

We use microprobe Angle-Resolved Photoemission Spectroscopy to study the Fermi surface and band dispersion of the CuO2 planes in the high temperature superconductor, YBa2Cu4O8. We find a strong in-plane asymmetry of the electronic structure between directions along a and b axes. The saddle point of the antibonding band lies at a significantly higher energy in the a direction (pi,0) than the b direction (0,pi), whereas the bonding band displays the opposite behavior. We demonstrate that the abnormal band shape is due to a strong asymmetry of the bilayer band splitting, likely caused by a non-trivial hybridization between the planes and chains. This asymmetry has an important implication for interpreting key properties of the Y-Ba-Cu-O (YBCO) family, especially the superconducting gap, transport and results of inelastic neutron scattering.