Two-dimensional vortex behavior in highly underdoped YBa_2Cu_3O_{6+x} observed by scanning Hall probe microscopy

TL;DR

This study uses scanning Hall probe microscopy to observe unique vortex behaviors in highly underdoped YBa_2Cu_3O_{6+x}, revealing sub-flux quantum flux bundles that are more mobile and prevalent at lower critical temperatures.

Contribution

It provides direct imaging evidence of kinked stacks of pancake vortices in underdoped YBa_2Cu_3O_{6+x}, a phenomenon not previously visualized.

Findings

Observation of flux bundles with less than one flux quantum

Increased mobility of these flux features compared to conventional vortices

Greater occurrence of sub-Φ_0 features at lower T_c

Abstract

We report scanning Hall probe microscopy of highly underdoped superconducting YBa_2Cu_3O_{6+x} with T_c ranging from 5 to 15 K which showed distinct flux bundles with less than one superconducting flux quantum (Phi_0) through the sample surface. The sub-Phi_0 features occurred more frequently for lower T_c, were more mobile than conventional vortices, and occurred more readily when the sample was cooled with an in-plane field component. We show that these features are consistent with kinked stacks of pancake vortices.