Anomalous flux quantization and formation of dipole-flux state in a multiply-connected high-Tc NdBa2Cu3O7-d superconductor

TL;DR

This study uses SQUID microscopy to explore flux quantization in anisotropic high-Tc NdBa2Cu3O7-d superconductors, revealing unique flux behaviors and a dipole-flux state linked to their anisotropic order parameter.

Contribution

It provides new insights into flux quantization and dipole-flux formation in anisotropic high-Tc superconductors, highlighting effects of geometry and magnetic field.

Findings

Non-uniform flux distribution in holes

Development of local magnetic dipole flux above 10μT

Flux quantization transitions depend on hole size

Abstract

High-resolution scanning superconducting quantum interference device (SQUID) microscopy was used to study the flux quantization phenomenon in multiply-connected anisotropic high-Tc NdBa2Cu3O7-d single crystalline thin films. The spatial distribution of internal flux in a hole was found to be non-uniform and changed drastically for applied small fields. With increased fields above 10uT, a local magnetic dipole flux developed inside the hole, in contrast to an isotropic Nb superconductor. The total net flux trapped in a hole was kept to be constant for larger holes, but the abrupt transition of flux quantization state was observed for smaller holes. The possible explanation is given based on the anisotropic dx2-y2-wave order parameter of high-Tc superconductors.