HEISENBERG SPIN CHAIN WITH MANY IMPURITIES

We consider the Heisenberg chain of spin 1/2 with a concentration x of impurity spins S. The thermodynamic Bethe ansatz equations are stated for this model. The ground-state equations are analyzed as a function of x and magnetic field. In zero field the ground state is a singlet for finite x, but non-Fermi-liquid-like for x --> 0. Two energy bands play a role at T = 0. The Van Hove singularities of the empty bands de fine two critical fields, H(c1)(x) and H(c2)(x), at which the suscepti bility diverges. The non-Fermi-liquid behavior as x --> 0 arises from nonanalyticities as H(c2) vanishes.