Tunnelling of Quantum Spins

Abstract

A WKB formalism is presented to describe the quantum dynamics, including tunnelling, of a single spin with large spin quantum number. This is of particular relevance to the treatment of Hamiltonians with a large anisotropy. For a wide class of Hamiltonians we obtain the eigenstates and tunnelling rates and show the universal dependence of the latter upon the spin quantum number, anisotropy and transverse fields.