Hidden, one-dimensional, strongly nested, and almost half-filled Fermi surface in Ba$_2$CuO$_{3+y}$ superconductors

TL;DR

This study uncovers a unique bilayer structure in Ba$_2$CuO$_{3+y}$ with a strongly nested, half-filled quasi 1D band, suggesting a different mechanism for superconductivity compared to traditional cuprates.

Contribution

It reveals a bilayer structure with a nested quasi 1D band in Ba$_2$CuO$_{3+y}$, highlighting a new electronic configuration linked to its superconductivity.

Findings

Identification of a bilayer structure with quasi 2D and 1D character.

Discovery of an almost half-filled, strongly nested quasi 1D band.

Correlation-induced inter-layer self-doping leading to unique electronic properties.

Abstract

All previous cuprate superconductors display a set of common features: (i) vicinity to a Cu 3$d^{9}$ configuration; (ii) separated CuO$_2$ planes; (iii) superconductivity for doping $\delta \sim$ 0.1$-$0.3. Recently [PNAS {\bf 24}, 12156 (2019)] challenged this picture by discovering "highly overdoped" superconducting Ba$_2$CuO$_{3+y}$. Using density-functional theory + dynamical mean-field theory, we reveal a bilayer structure of Ba$_2$CuO$_{3.2}$ of alternating quasi 2D and quasi 1D character. Correlations tune an inter-layer self-doping leading to an almost half-filled, strongly nested quasi 1D $d_{b^2-c^2}$ band, which is prone to strong antiferromagnetic fluctuations, possibly at the origin of superconductivity in Ba$_2$CuO$_{3+y}$.