Observation of Andreev bound states in bicrystal grain-boundary Josephson junctions of the electron doped superconductor LaCeCuO

TL;DR

This study reports the detection of Andreev bound states in grain-boundary Josephson junctions of LaCeCuO, indicating a d-wave symmetry of its superconducting order parameter through tunneling spectra analysis.

Contribution

It provides experimental evidence of Andreev bound states in electron-doped cuprate superconductors, supporting the d-wave pairing symmetry hypothesis.

Findings

Zero-bias conductance peak observed in tunneling spectra.

Magnetic field shifts the spectral weight consistent with Doppler effect.

ZBCP appears with the onset of superconductivity.

Abstract

We observe a zero-bias conductance peak (ZBCP) in the ab-plane quasiparticle tunneling spectra of thin film grain-boundary Josephson junctions made of the electron doped cuprate superconductor LaCeCuO. An applied magnetic field reduces the spectral weight around zero energy and shifts it non-linearly to higher energies consistent with a Doppler shift of the Andreev bound states (ABS) energy. For all magnetic fields the ZBCP appears simultaneously with the onset of superconductivity. These observations strongly suggest that the ZBCP results from the formation of ABS at the junction interfaces, and, consequently, that there is a sign change in the symmetry of the superconducting order parameter of this compound consistent with a d-wave symmetry.