Scanning tunneling microscopy of the <i>a</i>-<i>b</i> planes of Bi2(Ca,Sr)3Cu2O8+δ single crystal and thin film

Abstract

A scanning tunneling microscope was used to image the a-b plane of a single crystal of Bi2(Ca,Sr)3Cu2O8+δ (Tc∼85 K) and a thin film grown epitaxially on a (100) SrTiO3 substrate. Images taken at room temperature in air of a freshly cleaved bulk sample clearly show the one-dimensional superstructure (27.2±0.7 Å periodicity) which is common to this phase. Several images show steps 16 Å high, suggesting that the cleavage occurs between 2122 molecular units. The registry of the superstructure from terrace to terrace is either shifted by half a superlattice parameter or is aligned. Images of evaporated thin films show features of comparable size, but not the same long-range order as the crystal. Low-temperature conductance measurements of the thin film exhibit a BCS-like energy gap with 2Δ/kTc≊12.