Drude-like Peak Research Articles

Optical conductivity of the Hubbard and t-J models.

We calculate the optical conductivity \ensuremath{\sigma}(\ensuremath{\omega}) of the Hubbard and t-J models on 10- and 16-site lattices, respectively, using a Lanczos method. Results are presented for various values of the couplings U/t, J/t, and band fillings, using free- and periodic-boundary conditions. We discuss the behavior of the kinetic energy in the ground state, the distribution of spectral weight of \ensuremath{\sigma}(\ensuremath{\omega}) between low and high energies and the sum rule. Indications of a Drude-like peak at low energy in the one-hole subspace are observed in both models. Assuming that holes behave like independent (mass-renormalized) particles in the normal state of the superconductors, our results also suggest that the optical midinfrared broadband observed experimentally can be explained by hole excitations of strongly correlated systems.

Far-infrared optical properties of Bi2Sr2CaCu2O8.

The reflectance of crystals of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ has been measured in the far-infrared region at 100 K in the normal state and at 1.5 K in the superconducting state. The normal-state optical properties are dominated at low frequency by a narrow Drude-like peak in the real part of the optical conductivity. At higher frequency there is substantial absorption above this Drude absorption that can be parametrized with two broad oscillators centered at roughly 400 and 1000 cm/sup -1/ in the optical conductivity. In the superconducting state there is a sharp reflectance edge at 300 cm/sup -1/ associated with a threshold in the real part of the optical conductivity, but it is not certain that this is a conventional energy gap.