Cuprate superconductivity emerges in the copper oxide plane by doping the charge reservoir layers, while the undoped copper oxide is well known as a Mott insulator. How the carriers are transferred from the doped charge reservior layers into the intact CuO2 planes remains to be elucidated. In 2012 we disovered the interface-enhanced superconductivity in single unit-cell FeSe/SrTiO3 system and also pointed out that the high transition temperature of the layered cuprates may very likely result from a single unit cell of the material. Meanwhile, in order to unravel the underlying physics in cuprate superconductors, it is highly tempting to investigate directly the copper oxide plane in experiment.

Among all cuprate compounds infinite layer cuprates have the simplest crystal structure and also can be prepared with a CuO2-terminated surface. By using molecular beam epitaxy and scanning tunneling microscopy techniques we have conducted the direct measurement of the CuO2 plane upon doping in infinite layer cuprates, promising a more profound comprehension of cuprate superconductivity through the lens of the CuO2 surface.