The broad band spectrum of the optical conductivity of the quasi-one dimensional organic conductor (FA)2PF6 (FA = fluoranthene) has been investigated in a wide temperature range including the Peierls transition temperature Tp = 180 K. A semiconducting gap has been observed both below and above Tp varying between 150 meV at 10 K and 80 meV at 300 K. The (Tp − T)14 temperature dependence for the order parameter has been deduced from an analysis of the integrated band intensity of phase phonons thus giving evidence that the Peierls transition is a 2nd order phase transition near the tricritical point.

The broad band spectrum of optical conductivity of the quasi one-dimensional organic conductor (FA)2PF6 has been investigated in a wide temperature range including the Peierls transition temperature Tp = 180 K. The semiconducting gap value has been observed both at 10 K (∼143 meV) and at 300 K (∼80 meV). We show in the present study that in contrast to the dc conductivity the electronic part of dynamical conductivity at energies 0.02–0.06 eV is mainly driven by 1-D fluctuations in a wide temperature range and does not show any distinct crossover to 3-D behavior below Tp , while this crossover is certainly observed in the temperature dependence of the intensity of intramolecular vibrations. From the latter the temperature dependence of the order parameter for the Peierls transition has been determined to be Δ(T) ∼ (Tp — T)1/4 what is characteristic for a second order phase transition near tricritical point.

We have determined the reflectance of the misfit layer compounds 'LnNb2X5' (Ln identical to Y, Nd or La; X identical to S or Se) between 50 meV and 6 eV for the electric field parallel to the layers. By fitting a Lorentz-Drude model the spectral distribution of the components of the energy loss function and of the conductivity function parallel to the layers were obtained. On the assumption of a charge transfer from the mod LnX mod to the mod NbX2 mod layers the values of the effective mass could be calculated from the intraband contribution to the optical spectra.

We have determined the longitudinal optical conductivity of (TaSe4)2I in the energy range from 50 meV to 2 eV at different temperatures between 15 K and 420 K. We find a clear evidence that the free carriers are condensed into a charge density wave ground state not only below the transition temperature of 263 K but also at higher temperature up to the limits of the chemical stability of this compound.

Thin films of superconducting YBa2Cu3O7-δ (Tc ≈ 90 K), deposited on Al2O3, have been used to study reflection and absorption from 0.15 to 6 eV. Values for charge transfer gaps are found near 4 and 5 eV. In the weak-absorption region below 4 eV there appear broad maxima near 0.6, 1.5 and 3 eV–very similar to the well-known d-d transitions in the magnetic oxides of the 3d transition metals.

The reflectance spectra of polycrystalline La2−xSr x CuO4 samples were investigated in the energy range between 50 meV and 4 eV in dependence of the Sr content. The spectra are attributed to free carrier absorption of the Drude type, superimposed by optical phonon excitations below 0.1 eV and intrinsic absorption above 1 eV. From the influence of Sr doping onto the plasma energy it is deduced that La2−xSr x CuO4 is ap-type conductor with a maximum carrier concentration of 2.0×1021 cm−3 forx=0.15. The results are interpreted in terms of a Hubbard model with an empty upper and ap-doped lower Hubbard band with a width of 1.9 eV.

Thin films and single crystals of YBa 2 Cu 3 O 7-δ have been used to study absorption and/or reflectance in the energy range from 0.15 to 6 eV. The observed spectra are attributed to free carrier absorption, to d-d transitions within the d9 Cull configuration and to charge transfer excitations.

Thin films and single crystals of YBa 2 Cu 3 O 7-δ have been used to study absorption and/or reflectance in the energy range from 0.15 to 6 eV. The observed spectra are attributed to free carrier absorption, to d-d transitions within the d9 Cull configuration and to charge transfer excitations.

We report the reflectance spectra of pressed powder samples of the high-temperature superconductor La1.85Sr0.15CuO4 and of La2CuO4 in the energy range beteween 30 meV and 6 eV. The spectrum of the superconducting compound differs remarkably from those of conventional metals. It shows a plasma edge in the near infrared with a plasma energy of ℏωp = 0.8 eV and optical phonons up to an energy of 90 meV. The optical results yield a very low carrier concentration of 1.7 x 1021cm3.

The polarized reflectance spectra obtained on NbSe3 and TaSe3 reveal a two-dimensional metallic behaviour in both compounds. It results, however, from the evaluation of the spectra that the electrical anisotropy within the plane of metallic conduction in NbSe3 is considerably higher than in TaSe3.

(TaSe4)2I is a one-dimensional conductor exhibiting a charge-density-wave transition at 263 K which is accompanied by non-linear effects of the electrical conductivity. The electrical anisotropy was confirmed previously by optical measurements which had shown a pronounced plasma edge for light polarized parallel to the metallic chains and a nearly constant reflectivity for the polarization direction perpendicular to the chain axis. The present extended optical investigations reveal a Peierls gap existing even at room temperature. The temperature dependence of this gap in the temperature range between 140 K and 420 K is reported and the consequences for the electrical transport properties are discussed.

The cluster compound Tl2Mo6Se6 shows a superconducting transition although the crystal structure and the electrical conduction indicate a highly one-dimensional metallic behaviour. We have investigated by optical methods the transport properties of Tl2Mo6Se6 parallel and perpendicular to the metallic axis, by measuring the polarized reflectance spectra in the energy range between 0.05 and 6 eV. The results confirm the high electrical anisotropy of Tl2Mo6Se6, thereby constituting a contrast to previous results obtained on the polymeric superconductor (SN)x.

The polarized reflectance spectra of NbSe3 and (TaSe4) and 300 K are reported. The experimental data are analyzed in terms of a Lorentz-Drude and a tight binding model.

The optical reflectance of NbSe3 single crystals was investigated in the energy range between 0.15 and 5 eV under irradiation with polarized light. For light polarized perpendicular to the metallicaxis the crystals exhibit the optical behaviour of a semiconductor, whereas for light polarized parallel to the metallic axis a strongly damped plasma edge below 1 eV is observed. The experimental data are analyzed in terms of a Lorentz-Drude model in order to determine the electrical conductivity, the effective mass and the collision time of the free carriers, the width of the conduction band, and the contribution of interband absorption.

AbstractPolarized reflectance spectra of (SN)x single crystals are investigated in the range from 0.15 to 4 eV. For light polarized parallel to the polymeric chains the Drude behaviour found previously is confirmed. The optical properties perpendicular to the chains, however, are explained by a modified Maxwell‐Garnett model. This model takes into account the fibrous structure of (SN)x crystals and allows to separate the intrinsic and extrinsic transverse transport properties.

In previous work we have observed the amplitude mode of the charge density wave (CDW) in K2Pt(CN)4Br0.3⋯3.2H2O (KCP) by means of Raman scattering. New measurements made on deuterated material, K2Pt(CN)4Br0.3⋯3.2D2O (KCP∗), show the same mode but shifted from 44 to 38 cm−1, maintaining the symmetry properties and temperature dependence of frequency and linewidth. This considerable isotope effect is interpreted in terms of a coupling of the CDW with the water stretching mode, which by the deuteration is shifted from 3494 cm−1 in KCP to 2560 cm−1 in KCP∗ according to the change in atomic mass. Both of these modes exhibit A1(z) symmetry. At 5 K the resulting decoupled frequency of the CDW amplitude mode is 57 cm−1, and the coupling energy about 140 cm−1. A discussion of the temperature dependence of various important quantities is given. The present results show that the water molecules, which are located in between the Pt chains are strongly involved in the eigenvector of the CDW amplitude mode.