Functional integral quantisation of an anisotropic spin-field model

The authors develop a path-integral formalism to obtain the semiclassical quantum spectrum of the pulse soliton with an internal degree of freedom in the one-dimensional continuous Heisenberg ferromagnet with an easy axis. No restriction is imposed on the spin magnitude S. For S=1/2, the pulse soliton yields the same quantum spectrum as that of the S=1/2 lattice Heisenberg-Ising ferromagnet obtained by the Bethe ansatz method. This agreement supports a plausible particle picture of the multimagnon bound state. For S>1/2, the present semiclassical spectrum can also be interpreted, aside from its prefactor, in terms of an underlying spin S(>1/2) quantum lattice model if the cut-off condition for the wave-number of the soliton is taken into account.