OBSERVATION OF LARGE TUNNELING-CONDUCTANCE VARIATIONS IN DIRECT MAPPING OF THE ENERGY-GAP OF SINGLE-CRYSTAL BI2SR2CACU2O8-X

The tunneling conductance G(V,x,y) is mapped with 5 angstrom resolution on cleaved a-b planes of Bi2Sr2CaCu2O8-x crystals (T(c) = 90 K) using scanning (vacuum) tunneling spectroscopy at 4.2 K. A strong, spatially varying G(V,x,y), evidently arising from a superconducting gap DELTA(c), is observed on the a-b plane. A more highly peaked G ( V) with reduced peak spacing is seen near (approximately 50 angstrom) specific sites, and over broader areas. It is suggested that the striking variations in G (V,x,y) probably indicate local variations in BiO-layer metallicity, revealing an internal superconducting proximity effect between BiO and CuO2 layers.