SPECIFIC-HEAT OF THE IMPURE SPIN-1 2 XY CHAIN

We use a pseudofermion representation to investigate strong-field anom alies of the magnetic-field (h) dependence of the specific heat (c) of a spin-1/2 XY chain doped with magnetic impurities. If at certain mag netic field the impurity-induced split-off energy levels come sufficie ntly close to the chemical potential of pseudofermions (zero), then at low temperatures the specific heat of the chain is significantly alte red by even a small number of impurities. The impurity-induced peaks o f the c (h) dependence correspond to magnetic fields in a range where the specific heat of the ideal spin-1/2 XY chains is exponentially sma ll. They have the same physical origin, but different structure, as co mpared to the high-field anomalies of longitudinal magnetic susceptibi lity investigated previously.