Modifying the surface electronic properties of YBa₂Cu₃O_7-δ with cryogenic scanning probe microscopy

We report the results of a cryogenic study of the modification of YBa₂Cu₃O_7-δ surface electronic properties with the probe of a scanning tunnelling microscope (STM). A negative voltage applied to the sample during STM tunnelling is found to modify locally the conductance of the native degraded surface layer. When the degraded layer is removed by etching, the effect disappears. An additional surface effect is identified using scanning Kelvin probe microscopy in combination with STM. We observe reversible surface charging for both etched and unetched samples, indicating the presence of a defect layer even on a surface never exposed to air.