Accurate Determination of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mfrac><mml:mrow><mml:mn>2</mml:mn><mml:mi>e</mml:mi></mml:mrow><mml:mrow><mml:mi>h</mml:mi></mml:mrow></mml:mfrac></mml:math>in Y-Ba-Cu-O Josephson Junctions

Accurate measurements of $\frac{2e}{h}$ by means of the ac Josephson effect have been carried out by the use of weak links of a high-${T}_{c}$ superconductor, Y-Ba-Cu-O, of macroscopic dimensions. The result, $\frac{2e}{h}=483595.0\ifmmode\pm\else\textpm\fi{}1.7$ GHz/V, differs, in relative value, from that obtained by accurate measurements in metallic superconductors by 5.6 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}6}$.