Electromagnetic properties at the grain boundary interface of a ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ bicrystal Josephson junction

Electromagnetic resonances along a ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ bicrystal grain boundary junction made it possible to determine the ratio between the barrier/boundary thickness and the relative dielectric constant ${\mathit{t}}_{\mathit{d}}$/${\mathrm{\varepsilon }}_{\mathit{r}}$, the London penetration depth ${\lambda }_{\mathit{L}}$, and to estimate the surface resistance ${\mathit{R}}_{\mathit{s}}$ at the interfaces of the grains. From resonances at 256–638 GHz, their Q values, and the Stewart-McCumber parameter, we find ${\mathit{t}}_{\mathit{d}}$/${\mathrm{\varepsilon }}_{\mathit{r}}$≊0.4 nm, ${\lambda }_{\mathit{L}}$=140±30 nm, and ${\mathit{R}}_{\mathit{s}}$∼20 mΩ at f=280 GHz. This indicates that the boundary is dielectric, and that the grains are well superconducting within 5–20 nm from the boundary interfaces.