# Buried double CuO chains in YBa$_2$Cu$_4$O$_8$ uncovered by nano-ARPES

## TL;DR

This study uses nano-ARPES to uncover the electronic structure of buried double CuO chains in YBa2Cu4O8, revealing metallic dispersions and Fermi surfaces that are highly one-dimensional but lack strong electron correlations.

## Contribution

First observation of the electronic structure of buried double CuO chains in YBa2Cu4O8 using spatially-resolved nano-ARPES, clarifying their metallic nature and surface termination effects.

## Key findings

- Buried CuO chains exhibit sharp metallic dispersions.
- Fermi surfaces are highly one-dimensional.
- No evidence of strong electron correlations or Luttinger liquid behavior.

## Abstract

The electron dynamics in the CuO chains has been elusive in Y-Ba-Cu-O cuprate systems by means of standard angle-resolved photoemission spectroscopy (ARPES); cleaved sample exhibits areas terminated by both CuO-chain or BaO layers, and the size of a typical beam results in ARPES signals that are superposed from both terminations. Here, we employ spatially-resolved ARPES with submicrometric beam (nano-ARPES) to reveal the surface-termination-dependent electronic structures of the double CuO chains in YBa$_2$Cu$_4$O$_8$. We present the first observation of sharp metallic dispersions and Fermi surfaces of the double CuO chains buried underneath the CuO$_2$-plane block on the BaO terminated surface. While the observed Fermi surfaces of the CuO chains are highly one-dimensional, the electrons in the CuO-chains do not undergo significant electron correlations and no signature of a Tomonaga-Luttinger liquid nor a marginal Fermi liquid is found. Our works represent an important experimental step toward understanding of the charge dynamics and provides a starting basis for modelling the high-$T_c$ superconductivity in YBCO cuprate systems.