Spectral properties of a non-degenerate polaron gas

We apply the dynamic mean field theory to calculate the low-density limit o f the small polaron optical conductivity in the Holstein model. Classical s chemes of approximation are recovered in weak coupling and in the adiabatic and anti-adiabatic strong coupling limits. Such schemes are not suitable f or the intermediate coupling regime, where our theory gives an anomalous in crease of the spectral weight at low energy as the temperature decreases. T his result could be relevant to interpret some features observed in MIR and FIR optical conductivity of the oxide compounds. (C) 2000 Elsevier Science B.V. All rights reserved.