SPIN-WAVES IN A SURFACE-DILUTED QUANTUM SPIN SYSTEM

A theoretical investigation of the effects of surface dilution on spin waves in a semi-infinite transverse Ising model (TIM) is presented. W ithin the framework of the double-time Green's function theory, the lo cal density of spin-wave states is obtained by the application of the cluster-Bethe-lattice (CBL) method. Numerical calculations of paramagn etic phases reveal that surface dilution will lead to appearance of th e localized spin-wave states whose frequencies are bulk independent wh ile the corresponding density of states is a function of the exchange interactions. Increase of the bulk exchange interactions between the s urface and the bulk spins tends to diminish the localized spin-wave st ates. Dependence of the local density of states on the concentration p of the magnetic atoms is similar with that in a three-dimensional inf inite TIM which has been discussed in our previous paper.