Investigation of the energy gap of Y-Ba-Cu-O by point-contact Josephson-junction techniques

Experimental results on stable point-contact Nb/Y-Ba-Cu-O structures are reported. Reproducible current-voltage characteristics showing Josephson coupling are obtained. Measurements of $\frac{\mathrm{dV}}{\mathrm{dI}}$ give an estimate for the energy-gap value of the high-$T_c$ superconductor Y-Ba-Cu-O $\Delta =19.5\mathrm{}\pm 2.0$ mV, corresponding to a ratio $\left[\frac{2\Delta \mathrm{}\left(0\right)\mathrm{}}{k_B{T}_c}\right]=4.8\mathrm{}$ in agreement with previous results obtained by a different technique.