Square vortex lattice at anomalously low magnetic fields in electron-doped Nd$_{1.85}$Ce$_{0.15}$CuO$_{4}$

TL;DR

This study presents the first direct observation of a square vortex lattice in electron-doped Nd$_{1.85}$Ce$_{0.15}$CuO$_{4}$, revealing its persistence at low magnetic fields and its consistency with d-wave superconductivity theories.

Contribution

First direct bulk observation of a square vortex lattice in electron-doped cuprate, showing its stability at low magnetic fields and aligning with d-wave gap models.

Findings

Square vortex lattice observed with 45° orientation.

Persistence of square symmetry at low magnetic fields.

Rapid decrease in vortex lattice diffraction intensity with increasing field.

Abstract

We report here on the first direct observations of the vortex lattice in the bulk of electron-doped Nd$_{1.85}$Ce$_{0.15}$CuO$_{4}$ single crystals. Using small angle neutron scattering, we have observed a square vortex lattice with the nearest-neighbors oriented at 45$^{\circ}$ from the Cu-O bond direction, which is consistent with theories based on the d-wave superconducting gap. However, the square symmetry persists down to unusually low magnetic fields. Moreover, the diffracted intensity from the vortex lattice is found to decrease rapidly with increasing magnetic field.