Three-tunnel-capacitor model for single-electron tunneling in layered thin films.

Abstract

Measurements of the tunnel current as a function of applied voltage on the layered high-${\mathit{T}}_{\mathit{c}}$ material ${\mathrm{TlBa}}_{2}$(${\mathrm{Ca}}_{0.8}$${\mathrm{Y}}_{0.2}$)${\mathrm{Cu}}_{2}$${\mathrm{O}}_{7}$ have been shown to exhibit single-electron tunneling behavior. It has been proposed that the ultrasmall capacitance required to explain the single-electron tunneling spectra obtained with a low-temperature scanning tunneling microscope arises naturally from the planar crystal structure of this high-${\mathit{T}}_{\mathit{c}}$ material. This hypothesis is further examined using a single-electron tunneling model that incorporates three tunnel capacitors, a condition that is required by atomic-force-microscope studies of the topography of the film's surface. An improved fit to the tunneling conductance is obtained, providing further evidence that a key to understanding Coulomb blockade in layered materials like ${\mathrm{TlBa}}_{2}$(${\mathrm{Ca}}_{0.8}$${\mathrm{Y}}_{0.2}$)${\mathrm{Cu}}_{2}$${\mathrm{O}}_{7}$ is the tunnel capacitors that form between multilayer CuO planes. This conclusion has important implications for the fabrication of nanoelectronc devices based on single-electron effects.