Non-quantized Dirac monopoles and strings in the Berry phase of anisotropic spin systems

TL;DR

This paper explores the Berry phase in anisotropic spin systems, revealing it comprises geometric and topological parts linked to non-quantized Dirac monopoles and strings, with implications for experimental physics.

Contribution

It introduces a novel interpretation of the Berry phase involving non-quantized Dirac monopoles and strings in anisotropic spin systems.

Findings

Berry phase includes geometric and topological contributions.

Identification of non-quantized Dirac monopoles and strings.

Discussion of experimental implications of the effect.

Abstract

The Berry phase of an anisotropic spin system that is adiabatically rotated along a closed circuit C is investigated. It is shown that the Berry phase consists of two contributions: (i) a geometric contribution which can be interpreted as the flux through C of a non-quantized Dirac monopole, and (ii) a topological contribution which can be interpreted as the flux through C of a Dirac string carrying a non-quantized flux, i.e., a spin analogue of the Aharonov-Bohm effect. Various experimental consequences of this novel effect are discussed.