Transitions at avoided level crossing with interaction and disorder

TL;DR

This paper studies how interactions and disorder affect avoided-level-crossing transitions in quantum systems, revealing deviations from mean-field predictions especially for dipole-dipole interactions in molecular magnets.

Contribution

It provides new insights into the effects of disorder on transition suppression or enhancement in systems with dipole-dipole interactions, beyond mean-field approximations.

Findings

Dipole-dipole interactions cause large deviations from mean-field predictions.

Disorder can invert the effect of interactions on transition probabilities.

Shape and disorder influence the transition behavior in molecular magnets.

Abstract

We investigate the influence of interaction between tunneling particles and disorder on their avoided-level-crossing transitions in the fast-sweep limit. Whereas the results confirm expectations based on the mean-field arguments that ferromagnetic/antiferromagnetic couplings suppress/enhance transitions, we found large deviations from the mean-field behavior for dipole-dipole interactions (DDI) in molecular magnets Mn-12 and Fe-8. For ideal crystals of the needle, spherical, and disc shapes DDI tends to enhance transitions. This tendency is inverted for the needle shape in the presence of even small disorder in the resonance fields of individual particles, however.