Interfacial Superconductivity in Cu/Cu2O and its Effect on Shielding Ambient Electric Fields [arXiv]
A model is presented for two-dimensional superconductivity at semiconductor-on-metal interfaces mediated by Coulomb interactions between electronically-active interface charges in the semiconductor and screening charges in the metal. The junction considered is native Cu2O on Cu in which an interfacial double charge layer of areal density n, comprising superconducting holes in Cu2O and mediating electrons in Cu, is induced in proportion to a sub-monolayer of adsorbed 4He atoms. Evidence for superconductivity on copper with prior air exposure is revealed in new analysis of previously published work function data. Based on a theory developed for layered superconductors, the intrinsic transition temperature TC = β n1/2/ζ is determined by n and transverse distance ζ ≃ 2.0 Å between the charge layers; β = 1.933(6) e2ƛC/kB = 1247.4(3.7) K-Å2 is a universal constant involving the reduced Compton wavelength of the electron ƛC. This model is applied to understanding the shielding of copper work-function patch and gravitational compression electric fields reported in the Witteborn-Fairbank gravitational electron free fall experiment. Interfacial superconductivity with n ≃ 1.6 × 1012 cm−2, TC ≃ 7.9 K and Berezinskiĭ-Kosterlitz-Thouless temperature TBKT ≃ 4.4 K accounts for the shielding observed at temperature T ≃ 4.2 K. Helium desorption and concomitant decreases in n and TC replicate the temperature transition in ambient electric fields on falling electrons, as observed by Lockhart et al., and the vanishing of superconductivity above T ≃ 4.8 K.
Fig. 6. Ambient electric field inside copper tube vs. temperature. Filled symbols (LWF) denote data from Refs. [34] and [100]; open square symbol (WF) from Ref. [30]. Solid (red), dashed (green), and dotted (blue) curves are obtained with reduced normal-state resistance rN = 1.0, 0.5, and 1.5, respectively.
Dale R. Harshman and Anthony T. Fiory, physics C: Superconductivity and its Applications (in press).
