Chain metallicity and competition between paramagnetism and antiferromagnetism in underdopedYBa2Cu3O6+x: A first principles description

Abstract

We describe, from advanced first principles calculations, the energetics of oxygen doping and its relation to insulator-metal transitions in underdoped ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{6+x}$. We find a strong tendency of doping oxygens to order into nonmagnetic ${\text{Cu}}^{1+}{\text{O}}_{x}$ chains at any $x$. Ordering produces one-dimensional metallic bands, while configurations with nonaligned oxygens are insulating. The ${\text{Cu}}^{2+}{\text{O}}_{2}$ 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 antiferroparamagnetic competition depends on $x$ but only weakly on the ordering state of the chains.