Comment on: Quantum interference of tunnel trajectories between states of different spin length in a dimeric molecular nanomagnet

TL;DR

This paper critically analyzes a previous study on quantum interference in a molecular nanomagnet, demonstrating data inconsistencies and limitations of the applied models, and emphasizing the importance of experimental conditions.

Contribution

It challenges the original interpretation by showing data inconsistencies, clarifies the applicability of the Landau-Zener formula, and questions the dimer model's validity in explaining the observed phenomena.

Findings

Published data are inconsistent and mostly incorrect.

Landau-Zener formula application is limited to specific experimental regions.

The observed transition cannot be explained by the dimer model.

Abstract

Ramsey et al. [Nature Phys. 4, 277-281 (2008)] report the observation of quantum interference associated with tunnelling trajectories between states of different total spin length in a dimeric molecular nanomagnet. They argue that the interference is a consequence of the unique characteristics of a molecular Mn12 wheel, which behaves as a molecular dimer with weak ferromagnetic exchange coupling. We show here that the data published by Ramsey et al. are not consistent and unfortunately mostly wrong. We show further that the Landau-Zener (LZ) formula, which links the tunnel probability with the tunnel splitting, can only be applied in a well-defined experimental region, which lays outside the region accessed by Ramsey and colleagues. Only a lower-limit estimate of the tunnel splitting can be obtained, showing that the observed transition cannot be explained with the dimer model. We also present other shortcomings of the paper questioning the dimer model, and that the alignment of the magnetic field is crucial for observing quantum interference.