ELEMENTARY EXCITATIONS FOR THE INTEGRABLE SPIN-S HEISENBERG CHAIN WITH AN IMPURITY SPIN

Elementary excitations for the integrable spin-S antiferromagnetic Hei senberg chain with an impurity spin S' are investigated by using the B ethe ansatz solution. Dressed holes are introduced in order to describ e the elementary excitation. The characteristic energy dependence of t he spectral density for the elementary excitation at zero temperature is discussed in connection with behaviour patterns of physical quantit ies. We extend our calculation for the elementary excitation to the ca se of finite temperatures, applying the method developed by Yang and Y ang for one-dimensional interacting boson systems. At finite temperatu res, in the case where S < S', the spectral density shows a divergence property at zero excitation energy irrespective of the temperature, w hereas in the case where S > S', the peak structure develops in the lo w-energy region as the temperature is decreased.