Direct observation of nanometer-scale pinning sites in (Nd$_{0.33}$,Eu$_{0.20}$,Gd$_{0.47}$)Ba$_2$Cu$_3$O$_{7-\delta}$ single crystals

TL;DR

This study visualizes nanometer-scale pinning sites in (Nd,Eu,Gd)Ba2Cu3O7−δ single crystals, revealing stripe-like structures and nonsuperconducting regions that could enhance understanding of vortex pinning in high-temperature superconductors.

Contribution

It provides direct observation of nanometer-scale pinning sites and stripe-like structures in these crystals, linking surface and bulk features to potential vortex pinning mechanisms.

Findings

Stripe-like structures observed on surface and in bulk.

Nonsuperconducting regions identified as pinning sites.

Periodicities range from 20 to 800 nm.

Abstract

We report on the observation of self-organized stripe-like structures on the as-grown surface and in the bulk of (Nd,Eu,Gd)Ba$_2$Cu$_3$O$_y$ single crystals. The periodicity of the stripes on the surface lies between 500 and 800 nm. These are possibly the growth steps of the crystal. Transmission electron microscopy investigations revealed stripes of periodicity in the range of 20 to 40 nm in the bulk. From electron back scattered diffraction investigations, no crystallographic misorientation due to the nanostripes has been found. Scanning tunneling spectroscopic experiments revealed nonsuperconducting regions, running along twin directions, which presumably constitute strong pinning sites.