Scanning tunnelling spectroscopy of an oxide superconductor Bi2Sr2CaCu2O8-δ

The authors carried out a tunnelling spectroscopy measurement on a single crystal of superconducting oxide Bi2Sr2CaCu2O8- delta using a low temperature scanning tunnelling microscope. The superconducting gap parameter shows a spatial variation over a relatively small area ( approximately 10 nm). The authors obtained the energy gap parameter Delta (4.2 K)=26 meV, the most observable value, and correspondingly 2 Delta /kBTc=7, larger than the BCS value. The shape of the (dI/dV)-V curve suggests an anisotropy of the energy gap. Thermal smearing of the gap structure is observed below Tc. Temperature dependence of the gap parameter is consistent with BCS. Even above Tc the conductance curve is not flat.