Superconductivity emerging from the N${\'e}$el state in ${\it infinite}$-${\it stage}$ single-layer cuprate La$_2$CuO$_{4+\delta}$

TL;DR

This study demonstrates that superconductivity can emerge from a uniform N${\'e}$el antiferromagnetic state in a single-layer cuprate with minimal excess oxygen, challenging previous notions about the relationship between magnetism and superconductivity.

Contribution

It reveals that superconductivity can coexist with a robust N${\'e}$el state in a single-layer cuprate, emphasizing the importance of uniform oxygen distribution and ordered magnetic states.

Findings

Superconductivity occurs in a uniform N${\'e}$el state with small carrier density.

Uniform oxygen distribution is crucial for phase coexistence.

Superconductivity can emerge from a magnetically ordered state.

Abstract

In copper oxides (cuprates) with single CuO$_2$ layer such as La$_{2-x}$Ba(Sr)$_x$CuO$_4$, antiferromagnetism coexists with superconductivity at small doping levels $x$, where chemical disorders are significant. Here, we report that superconductivity occurs in a uniform and fully ordered N${\'e}$el state in a single-layer cuprate La$_2$CuO$_{4+\delta}$ with a small amount of excess oxygen $(\delta = 0.015)$ as demonstrated by the $^{139}$La nuclear quadrupole resonance measurement. A uniform oxygen distribution in the crystal is crucial for achieving microscopic phase coexistence and overcoming the miscibility gap associated with the staging instability; self-organized periodic oxygen arrangement driven by mobile oxygen atoms. This finding prompts the reconsideration of superconductivity in cuprates, highlighting that it can emerge in a robust N${\'e}$el state that retains sizable magnetic moments and hosts only a small carrier density.