Size driven phase transitions in pinned vortex systems

TL;DR

This paper models three-dimensional vortex systems with surface pinning, revealing size-dependent phase transitions and reproducing experimental configurations without adjustable parameters.

Contribution

It introduces a Frenkel-Kontorova like model to predict vortex ground states and phase transitions based on sample thickness.

Findings

Identifies three distinct vortex phases with size-dependent stability.

Discovers a continuous transition from square to distorted hexagonal structure.

Finds a discontinuous transition from distorted to perfect hexagonal structure.

Abstract

We model a tridimensional vortex system in a sample with square superficial pinning in the top surface and obtain the ground state structures as a function of the sample thickness. Using a simple Frenkel-Kontorova like model and no adjustable parameters, we reproduce the experimental vortex configurations seen in the bottom surface and their range of stability. We find three phases with two transitions between them, including a continuous one from square to distorted hexagonal structure and a discontinuous one from distorted hexagonal to hexagonal structure.