Chain metallicity and antiferro-paramagnetism competition in underdoped YBa$_2$Cu$_3$O$_{6+x}$: a first principles description

TL;DR

This study uses first principles calculations to explore how oxygen doping influences electronic and magnetic properties in underdoped YBa₂Cu₃O₆₊ₓ, revealing chain ordering effects and a transition from antiferromagnetic insulator to paramagnetic metal.

Contribution

It provides a detailed first-principles analysis of oxygen doping effects, chain ordering, and magnetic transitions in underdoped YBa₂Cu₃O₆₊ₓ, highlighting the interplay between structure and electronic phases.

Findings

Oxygen dopants tend to form non-magnetic Cu¹⁺Oₓ chains.

Chain ordering induces one-dimensional metallic bands.

Cu²⁺O₂ planes remain insulating and antiferromagnetic up to a certain doping level.

Abstract

We describe from advanced first principles calculations the energetics of oxygen doping and its relation to insulator-metal transitions in underdoped YBa$_2$Cu$_3$O$_{6+x}$. We find a strong tendency of doping oxygens to order into non-magnetic Cu$^{1+}$O$_x$ chains at any $x$. Ordering produces one-dimensional metallic bands, while configurations with non-aligned oxygens are insulating. The Cu$^{2+}$O$_2$ planes remain insulating and antiferromagnetic up to a threshold between $x$=0.25 and 0.5, above which a paramagnetic normal-metal state prevails. The in-plane antiferro-paramagnetic competition depends on $x$, but only weakly on the ordering state of the chains.