Interfacial superconductivity in Cu/Cu${}_2$O and its effect on shielding ambient electric fields

Abstract

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 Cu${}_2$O on Cu in which an interfacial double charge layer of areal density $n$, comprising superconducting holes in Cu${}_2$O and mediating electrons in Cu, is induced in proportion to a sub-monolayer of adsorbed ${}^4\mathrm{He}$ 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 $T_{\mathrm{C}}$ = $\beta$ $n$${}^{1/2}$/$\zeta$ is determined by $n$ and transverse distance $\zeta$ $\simeq$ 2.0 $\mathring{\mathrm{A}}$ between the charge layers; $\beta$ = 1.933(6) $e$${}^2$$\bar{\lambda }$${}_{\mathrm{C}}$/k${}_{\mathrm{B}}$ = 1247.4(3.7) K-$\mathring{\mathrm{A}}$${}^2$ is a universal constant involving the reduced Compton wavelength of the electron $\bar{\lambda }$${}_{\mathrm{C}}$. 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 $n$ $\simeq$ 1.6 $\times$ 10${}^{12}$ ${\mathrm{cm}}^{-2},$ $T_{\mathrm{C}}$ $\simeq$ 7.9 K and Berezinskiĭ-Kosterlitz-Thouless temperature $T_{\mathrm{BKT}}$ $\simeq$ 4.4 K accounts for the shielding observed at temperature $T$ $\simeq$ 4.2 K. Helium desorption and concomitant decreases in $n$ and $T_{\mathrm{C}}$ replicate the temperature transition in ambient electric fields on falling electrons, as observed by Lockhart et al., and the vanishing of superconductivity above $T$ $\simeq$ 4.8 K.

arXiv comment20 pages, 9 figures, 18 equations, 111 references

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