Observation of two Andreev-like energy scales in La2-xSrxCuO4 superconductor-normal-metal-superconductor junctions

Conductance spectra measurements of highly transparent junctions made of superconducting La2-xSrxCuO4 electrodes and a nonsuperconducting La1.65Sr0.35CuO4 barrier are reported. At low temperatures below Tc, these junctions have two prominent Andreev-like conductance peaks with clear steps at energies Δ1 and Δ2 with Δ2>2Δ1. No such peaks appear above Tc. The doping dependence at 2 K shows that both Δ1 and Δ2 scale roughly as Tc. Δ1 is identified as the superconducting energy gap, while a few scenarios are proposed as for the origin of Δ2.