BERRYS PHASE AND QUANTUM DYNAMICS OF FERROMAGNETIC SOLITONS

We study spin parity effects and the quantum propagation of solitons ( Bloch walls) in quasi-one-dimensional ferromagnets. Within a coherent state path integral approach we derive a quantum field theory for nonu niform spin configurations. The effective action for the soliton posit ion is shown to contain a gauge potential due to the Berry phase and a damping term caused by the interaction between soliton and spin waves . For temperatures below the anisotropy gap this dissipation reduces t o a pure soliton mass renormalization. The quantum dynamics of the sol iton in a periodic lattice or pinning potential reveals remarkable con sequences of the Ferry phase. For half-integer spin, destructive inter ference between opposite chiralities suppresses nearest-neighbor hoppi ng. Thus the Brillouin zone is halved, and for small mixing of the chi ralities the dispersion reveals a surprising dynamical correlation. Tw o subsequent band minima belong to different chirality states of the s oliton. For integer spin the Ferry phase is inoperative and a simple t ight-binding dispersion is obtained. Finally it is shown that external fields can be used to interpolate continuously between the Bloch wall dispersions for half-integer and integer spin.