Buried double CuO chains in YBa2Cu4 O8 uncovered by nano-ARPES

Abstract

Identifying the electron dynamics in CuO chains has been elusive in Y-Ba-Cu-O (YBCO) cuprate systems when using standard angle-resolved photoemission spectroscopy (ARPES); a cleaved sample exhibits areas terminated by both CuO chains 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 a submicrometric beam (nano-ARPES) to reveal the surface-termination-dependent electronic structures of the double CuO chains in YBa2Cu4O8. We present an observation of sharp metallic dispersions and Fermi surfaces of the double CuO chains buried underneath the CuO2-plane block on a 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 or a marginal Fermi liquid is found. Our work represents an important experimental step toward understanding the charge dynamics and provides a starting basis for modeling the high-Tc superconductivity in YBCO cuprate systems.