Large-field versus discontinuous instantons in spin orientation tunneling

TL;DR

This paper analyzes tunnel splitting oscillations in magnetic molecules, showing that at high magnetic fields, the instanton solution is continuous, contrasting with previous models that included fourth order anisotropy which induced discontinuous instantons.

Contribution

It demonstrates that in a simplified model without fourth order anisotropy, only one continuous instanton exists at large magnetic fields, challenging earlier findings of discontinuous instantons.

Findings

At large magnetic fields, only one continuous instanton is present.

Discontinuous instantons are induced by fourth order anisotropy, which is absent in the simplified model.

The simplified model provides a different perspective on tunnel splitting oscillations.

Abstract

Tunnel splitting oscillations in magnetic molecules are reconsidered within the simplest model for the problem, which does not contain fourth order anisotropy. It is shown that at large magnetic field, there is only one instanton, and it is continuous. This is in contrast to the discontinuous instantons that are induced by the fourth order term [Ersin Ke\c{c}ecio\u{g}lu and A. Garg, Phys. Rev. Lett. {\bf 88}, 237205 (2002)].