Distinct Pairing Symmetries in $Nd_{1.85}Ce_{0.15}CuO_{4-y}$ and $La_{1.89}Sr_{0.11}CuO_{4}$ Single Crystals: Evidence from Comparative Tunnelling Measurements

TL;DR

This study compares the pairing symmetries of electron- and hole-doped cuprate superconductors using tunnelling spectroscopy, revealing an s-wave component in electron-doped NCCO and a d-wave in hole-doped LSCO.

Contribution

It provides direct tunnelling evidence of distinct pairing symmetries in NCCO and LSCO, highlighting an s-wave component in NCCO's superconductivity.

Findings

NCCO shows no zero bias conductance peak in both orientations.

LSCO exhibits a zero bias conductance peak in the nodal direction.

NCCO has an s-wave component with Δ/kBTc≈1.66.

Abstract

We used point-contact tunnelling spectroscopy to study the superconducting pairing symmetry of electron-doped $Nd_{1.85}Ce_{0.15}CuO_{4-y}$ (NCCO) and hole-doped $La_{1.89}Sr_{0.11}CuO_{4}$ (LSCO). Nearly identical spectra without zero bias conductance peak (ZBCP) were obtained on the (110) and (100) oriented surfaces (the so-called nodal and anti-nodal directions) of NCCO. In contrast, LSCO showed a remarkable ZBCP in the nodal direction as expected from a d-wave superconductor. Detailed analysis reveals an s-wave component in the pairing symmetry of the NCCO sample with $\Delta/k_BT_c=1.66$, a value remarkable close to that of a weakly coupled BCS superconductor. We argue that this s-wave component is formed at the Fermi surface pockets centered at ($\pm\pi$,0) and (0,$\pm\pi$) although a d-wave component may also exist.