Metastable Vortex Lattice Phases in Superconducting MgB2

TL;DR

This study reveals highly metastable vortex lattice phases in MgB2 superconductors, enabling structural analysis of non-equilibrium states and suggesting domain jamming as a stabilization mechanism.

Contribution

First observation of metastable vortex lattice states in MgB2, allowing structural studies of non-equilibrium configurations in superconductors.

Findings

Discovery of metastable vortex lattice states in MgB2

Identification of a second-order rotation transition in VL

Speculation on domain jamming preventing ground state transition

Abstract

The vortex lattice (VL) symmetry and orientation in clean type-II superconductors depends sensitively on the host material anisotropy, vortex density and temperature, frequently leading to rich phase diagrams. Typically, a well-ordered VL is taken to imply a ground state configuration for the vortex-vortex interaction. Using neutron scattering we studied the VL in MgB2 for a number of field-temperature histories, discovering an unprecedented degree of metastability in connection with a known, second-order rotation transition. This allows, for the first time, structural studies of a well-ordered, non-equilibrium VL. While the mechanism responsible for the longevity of the metastable states is not resolved, we speculate it is due to a jamming of VL domains, preventing a rotation to the ground state orientation.