New Perspective on the Phase Diagram of Cuprate High-Temperature Superconductors

TL;DR

This paper links the charge distribution in CuO$_2$ planes, measured via NMR, to the Uemura relation, proposing a new phase diagram for cuprate superconductors and suggesting ways to enhance their critical temperature.

Contribution

It introduces a novel connection between orbital charge content and the Uemura scaling, leading to a new phase diagram and potential strategies to increase $T_c$ in cuprates.

Findings

Charge distribution correlates with $T_c$ across cuprate families.

Different cuprate families show distinct charge transfer behaviors.

Enhancing oxygen charge transfer to copper could raise $T_c$.

Abstract

Universal scaling laws can guide the understanding of new phenomena, and for cuprate high-temperature superconductivity such an early influential relation showed that the critical temperature of superconductivity ($T_c$) correlates with the density of the superfluid measured at low temperatures. This famous Uemura relation has been inspiring the community ever since. Here we show that the charge content of the bonding orbitals of copper and oxygen in the ubiquitous CuO$_2$ plane, accessible with nuclear magnetic resonance (NMR), is tied to the Uemura scaling. This charge distribution between copper and oxygen varies between cuprate families and with doping, and it allows us to draw a new phase diagram that has different families sorted with respect to their maximum $T_c$. Moreover, it also shows that $T_c$ could be raised substantially if we were able to synthesize materials in which more oxygen charge is transferred to the approximately half filled copper orbital.