QUANTUM TUNNELING OF SPIN PARTICLES IN PERIODIC POTENTIALS WITH ASYMMETRIC TWIN BARRIERS

The tunneling effect of a periodic potential with an asymmetric twin b arrier per period is calculated using the instanton method. The model is derived from the Hamiltonian of a small ferromagnetic particle in a n external magnetic field using the spin-coherent-state path integral. The instantons in two neighbouring barriers differ and lead to differ ent level shifts Delta epsilon(1), Delta epsilon(2). Using Bloch theor y we derive the energy spectrum which has formally the structure of an energy band, The spectrum depends on both level shifts. The removal o f Kramer's degeneracy by an external magnetic field is discussed, In a ddition we find a new kind of quenching of macroscopic quantum coheren ce which is irrelevant to Kramer's degeneracy.