Vortex Structure Around a Magnetic Dot in Planar Superconductors

TL;DR

This paper numerically investigates the vortex structures around a magnetic dot in superconductors, revealing how increasing magnetic moments favor higher flux vortex states and cause measurable fluctuations in magnetization.

Contribution

It provides a detailed numerical analysis of vortex states around magnetic dots in superconductors, highlighting the energetic favorability and experimental implications of higher flux quantum states.

Findings

Higher flux vortex states become energetically favorable with increased magnetic moment.

Vortex states become closer in energy, leading to magnetization fluctuations.

Physical quantities like magnetization can fluctuate with external magnetic fields.

Abstract

The problem of the giant vortex state around a magnetic dot which is embedded in a superconducting film is investigated. The full non-linear, self-consistent Ginzburg-Landau equations are solved numerically in order to calculate the free energy, the order parameter of the host superconductor, the internal magnetic field due to the supercurrents, the corresponding current density, the magnetization probed in the vicinity of the dot, and the normal electron density as a function of the various parameters of the system. We find that, as we increase the magnetic moment of the dot, higher flux quanta vortex states become energetically more favorable, as they can better compete with the external magnetic field via the Meissner effect. In addition to that, they progressively become closer to each other in energy with direct experimental consequences, i.e. physical quantities like magnetization may fluctuate when measured, for example, as a function of a uniform external magnetic field.