Fig. 4

Andreev spectroscopy of the superconducting energy gaps in an Au/YBCO heterostructure. (a) Conductance of a 100-nm-wide Au/YBCO nanoconstriction at T = 4.2 K. In the inset, an Au/YBCO constriction is presented as a parallel connection of two SNS junctions. A normal state area of the constrictions at the current above the critical current for YBCO and gold is shown in red and pink, respectively. (b) Temperature dependence of the normalized energy gaps in Au/YBCO heterostructure. The BCS model prediction is shown by the dashed black line. The inset shows the positions of the conductance dips indicated by dark-yellow arrows. The solid red line represents the V_n = 2Δ₁/ne dependence with Δ₁ = 14 meV.