Anomalous optical conductivity in disordered condensed matter

The real and imaginary optical conductivities in disordered semiconductors (and metals) do not follow classical Drudeʹs law in the near infrared region. We discuss an origin of the anomalous free carrier absorption in metallic (and near metallic) states of chalcogenide materials (phase-change GST), dye-sensitized nanocrystalline TiO2 and nanocrystalline silicon films. A series sequence of “localized” and “extended” state type behavior of carriers produces a Lorentz-type resonance which is caused by “bound” (localized) electrons. The analytical expressions were fit to the experimental data and produced various important physical parameters such as the numbers of free and localized carriers, the scattering time of free carriers, tunneling time of localized carriers, and the Drude dc conductivity in the system. We also discuss whether the present model has generated reasonable physical parameters.