La2CuO4

La2CuO4 is a copper oxide compound that serves as the parent compound of the La-based cuprate superconductors, such as La2−xSrxCuO4. It crystallizes in the K2NiF4-type layered perovskite structure, consisting of CuO2 planes separated by LaO layers. In this structure copper is formally Cu2+, and the spins in the CuO2 planes form a two-dimensional spin-1/2 antiferromagnetic lattice. The undoped material is a Mott insulator of the charge-transfer type, with strong electron correlations that localize carriers on copper sites.

At high temperature the crystal system is tetragonal; upon cooling it undergoes a structural distortion to an orthorhombic phase due to tilting of the CuO6 octahedra. The Néel temperature is about 325 K, below which long-range antiferromagnetic order develops.

Doping with divalent cations such as Sr2+ or Ba2+ substitutes for La3+ and introduces holes into the CuO2 planes. This suppresses antiferromagnetism and drives an insulator-to-metal transition, with superconductivity emerging at certain dopings. For La2−xSrxCuO4 the maximum Tc is around 38 K near x ≈ 0.15. The discovery of superconductivity in Ba- or Sr-doped La2CuO4-type compounds in 1986 helped inaugurate the era of high-temperature cuprates.

La2CuO4 is widely studied as a benchmark system for understanding correlation-driven physics in copper oxide superconductors and as a reference for the phase diagram of the cuprates.