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

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$\acute{e}$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$\acute{e}$el state that retains sizable magnetic moments and hosts only a small carrier density.

32 pages, 8 figures