DISORDER-ENHANCED DELOCALIZATION AND LOCAL-MOMENT QUENCHING IN A DISORDERED ANTIFERROMAGNET

The interplay of disorder and spin-fluctuation effects in a disordered antiferromagnet is studied. In the weak-disorder regime (W less than or equal to U), while the energy gap decreases rapidly with disorder, the sublattice magnetization, including quantum corrections, is found to remain essentially unchanged in the strong correlation limit. Magno n energies and Neel temperature are enhanced by disorder in this limit . A single paradigm of disorder-enhanced delocalization qualitatively accounts for all these weak disorder effects. Vertex corrections and m agnon damping, which appear only at order (W/U)(4), are also studied. With increasing disorder a crossover is found at W similar to U, chara cterized by a rapid decrease in sublattice magnetization due to quench ing of local moments, and formation of spin vacancies. The latter sugg ests a spin-dilution behavior that is indeed observed in softened magn on modes, lowering of Neel temperature, and enhanced transverse spin f luctuations.