title: Nonquantized dirac monopoles and strings in the berry phase of anisotropic spin systems.
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 nonquantized Dirac monopole, and (ii) a topological contribution which can be interpreted as the flux through C of a Dirac string carrying a nonquantized flux, i.e., a spin analogue of the Aharonov-Bohm effect. Various experimental consequences of this novel effect are discussed.
authors.affiliation: Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle, Germany. bruno@mpi-halle.de
authors.forename: Patrick
authors.initials: P
authors.lastname: Bruno