in the Two-dimensional Limit

Dimensionality plays a fundamental role in high-temperature superconductivity; all high-temperature superconductors adopt a layered crystal structure, and much of high-temperature superconductor theory is based on purely two-dimensional (2D) models. Here we exfoliate Bi₂Sr_2-xLa_xCuO_6+δ (referred to as La-Bi2201) single crystals down to monolayers (half unit cell) at liquid nitrogen temperature under ultra-high vacuum. A monolayer La-Bi2201 contains only a single layer of CuO₂ plane, and therefore represents a cuprate superconductor in the ultimate 2D limit. We study the electronic structure of monolayer La-Bi2201 at atomic scale using scanning tunnelling microscopy and spectroscopy.