Magnetic-force-microscope study of interlayer "kinks" in individual vortices in underdoped cuprate YBa$_2$Cu$_3$O$_{6+x}$ superconductor

TL;DR

This study uses magnetic force microscopy to image and manipulate individual vortices in a layered superconductor, revealing discrete pancake vortex stacks and their pinning forces, advancing understanding of vortex behavior in cuprates.

Contribution

It provides direct imaging and manipulation of vortex kinks in YBa₂Cu₃O₆.₄, confirming the discrete pancake vortex structure and quantifying pinning and coupling forces.

Findings

Vortices can break into discrete segments resembling pancake stacks.

Quantitative estimates of pinning forces and inter-stack coupling.

Observation of non-smooth tilting of vortices under manipulation.

Abstract

We use magnetic force microscopy to both image and manipulate individual vortex lines threading single crystalline YBa$_2$Cu$_3$O$_{6.4}$, a layered superconductor. We find that when we pull the top of a pinned vortex, it may not tilt smoothly. Sometimes, we observe a vortex to break into discrete segments that can be described as short stacks of pancake vortices, similar to the "kinked" structure proposed by Benkraouda and Clem. Quantitative analysis gives an estimate of the pinning force and the coupling between the stacks. Our measurements highlight the discrete nature of stacks of pancake vortices in layered superconductors.