Superconductivity emerging from the Neel state in infinite-stage single-layer cuprate La2CuO4+δ

The relationship between antiferromagnetism and superconductivity in copper oxide superconductors (cuprates) with single CuO ₂ conducting layer, e.g. La _{2- x} Ba(Sr) _x CuO ₄ , has been understood as a macroscopic phase separation when these phases appear in one sample. Here, we report compelling evidence that superconductivity occurs in a fully ordered Neel state as demonstrated by the ¹³⁹ La nuclear quadrupole resonance measurement for a single-layer cuprate La ₂ CuO _4+δ with small amount of excess oxygen δ = 0.015. Uniform oxygen distribution throughout the crystal is achieved as a crucial factor in realizing microscopic phase coexistence by surpassing the miscibility gap associated with the staging instability; self-organized periodic oxygen arrangement driven by mobile oxygen atoms. This finding urges the reconsideration of the superconducting phase diagram of cuprates and the mechanism underlying at. While there are similarities with iron-based and heavy-Fermion superconductors for two-phase coexistence, the presence of sizable magnetic ordered moments in the Nel state sets La ₂ CuO _4+δ apart.