Observation of two Andreev-like energy scales in $La_{2-x}Sr_{x}CuO_4$ superconductor/normal-metal/superconductor junctions

TL;DR

This study reports the observation of two distinct Andreev-like energy scales in La_{2-x}Sr_{x}CuO_4 superconductor junctions, revealing complex gap structures that scale with the critical temperature.

Contribution

It presents the first experimental evidence of two energy scales in LSCO junctions, with detailed analysis of their doping dependence and potential origins.

Findings

Two prominent conductance peaks at energies Δ₁ and Δ₂ below T_c

Both Δ₁ and Δ₂ scale with the critical temperature T_c

Δ₁ identified as the superconducting gap, Δ₂'s origin discussed

Abstract

Conductance spectra measurements of highly transparent ramp-type junctions made of superconducting $La_{2-x}Sr_{x}CuO_4$ electrodes and non superconducting $La_{1.65}Sr_{0.35}CuO_4$ barrier are reported. At low temperatures below $T_c$, these junctions have two prominent Andreev-like conductance peaks with clear steps at energies $\Delta_1$ and $\Delta_2$ with $\Delta_2 > 2\Delta_1$. No such peaks appear above $T_c$. The doping dependence at 2 K shows that both $\Delta_1$ and $\Delta_2$ scale roughly as $T_c$. $\Delta_1$ is identified as the superconducting energy gap, while a few scenarios are proposed as for the origin of $\Delta_2$.