Macroscopic quantum coherence in mesoscopic ferromagnetic systems

TL;DR

This paper investigates macroscopic quantum oscillations in ferromagnetic single domain magnets, revealing how external magnetic fields influence quantum level splitting and demonstrating interference effects akin to the Aharonov-Bohm phenomenon.

Contribution

It provides a theoretical analysis of MQO in ferromagnetic systems, including formulas for quantum tunneling at excited levels and the role of topological phases.

Findings

Level splitting oscillates with external magnetic field.

Quantum tunneling at excited levels is characterized.

Topological phase causes observable interference effects.

Abstract

In this paper we study the Macroscopic Quantum Oscillation (MQO) effect in ferromagnetic single domain magnets with a magnetic field applied along the hard anistropy axis. The level splitting for the ground state, derived with the conventional instanton method, oscillates with the external field and is quenched at some field values. A formula for quantum tunneling at excited levels is also obtained. The existence of topological phase accounts for this kind of oscillation and the corresponding thermodynamical quantities exhibit similar interference effects which resembles to some extent the electron quantum phase interference induced by gauge potential in the Aharonov-Bohm effect and the $\Theta $-vacuum in Yang-Mills field theory..