Optical Conductivity in Mott-Hubbard Systems

We study the transfer of spectral weight in the optical spectra of a strongly correlated electron system as a function of temperature and interaction strength. Within a dynamical mean field theory of the Hubbard model that becomes exact in the limit of large lattice coordination, we predict an anomalous enhancement of spectral weight as a function of temperature in the correlated metallic state and report on experimental measurements which agree with this prediction in $V_2O_3$. We argue that the optical conductivity anomalies in the metal are connected to the proximity to a crossover region in the phase diagram of the model.Comment: 12 pages and 4 figures, to appear in Phys. Rev. Lett., v 75, p 105 (1995

Observation of the Gap and Kinetic Energy in a Correlated Insulator

Fundamental energies are determined optically for an ensemble of correlated electrons in an anti-ferromagnetic insulator, V_2O_3. The observed variation of the energy gap and the kinetic energy are compared quantitatively to some approximate solutions of the Hubbard Hamiltonian

Temperature Dependence of Doping-Induced Modes in Cu-O Planes

Measurements of the frequency-dependent conductivity confirm that unusual lattice vibrational modes are induced by doping of several materials containing Cu-O planes. We find that the modes broaden rapidly with increasing temperature, consistent with the presence of a large linear component. This broadening of these vibrational modes is similar to that of electronic modes found previously in these same materials and analyzed in attempts to understand high-temperature superconductivity

Optical Properties of a Correlated Electron System: V_2O_3

The optical spectrum of V_2O_3 is found to resemble a Hubbard model system as described in an infinite-dimensional approximation. Assuming the validity of this comparison, we parameterize the effective Coulomb repulsive energy, the bandwith, and the mass enhancement. We suggest implicitly that these results should be compared with the cuprate and heavy Fermion superconductors

Scaling of an Infrared Absorption with Tc in a Cuprate Superconductor

We have studied the complex optical conductivity of Ba2YCu3O6+x crystals for

Reflectivity of Ba2YCu3O7-Σnormal State Dynamics

Measurements of reflectivity, R, as a function of temperature, T, and frequency, ω, in crystals of Ba2YCu3O7-δ, with σ ≅ 0.1, 0.3, and 0.8, are reported. The frequency dependent conductivity, σ(ω, T), obtained by analysis of R extrapolates at low ω to values consistent with previously reported σ(O,T). To explain the shape of σ(ω, T) requires the quasiparticle mass and lifetime to be strongly ω-dependent, withh¯/τ ≈ 2kBT and m*/mo ≈ 7 at low ω, crossingg over toh¯/τ ≈ 0.35 eV and m*/mo ≈ 1 forh¯/τ 〉 0.3 eV

Optical Excitations of a Few Charges in Cuprates

In studies of the optical spectrum of lightly doped semiconducting crystals containing CuO2 planes, we have observed absorption maxima that occur at the same energies as excitations in the superconducting phase of these materials. One structure occurs just above the phonon energies and near the antiferromagnetic exchange energy

The Energy Gap and Two-Component Absorption in a High Tc Superconductor

Edited by A. Bianconi (Pergamon Press, Oxford, 1989)