Charge Gap and Interchain Correlation in Quasi-One-Dimensional Dimerized Organic Conductors

Abstract

We study the relation between the charge gap and the interchain one-body correlation function in quasi-one-dimensional dimerized organic conductors at quarter filling, by applying the density matrix renormalization group method to a three-chain extended Hubbard model. The charge gap increases with the degree of dimerization in the intrachain hopping integrals. When the charge gap is larger than the interchain hopping integral, the interchain hopping correlation is strongly suppressed, as observed in the (TMTTF)₂X salts.     

Phase Transitions of A Quasi-One-Dimensional Fermi Gas

Phase transitions of a quasi-one-dimensional Fermi gas are studied by the use of the renormalization group method for the fermion system without the bosonization. Intrachain backward and forward scatterings, pair electron hopping between different chains and exchange scattering of electrons in different chains are taken account of. Pair electron hopping gives rise to the singlet and triplet superconductor phase transitions. Electron exchange scattering gives rise to the spin density wave and charge density wave transitions. Calculation is made by the use of the one-dimensional dispersion. Following Menyhárd's method (Ref. 1) for the model with interchain backward scattering only, the change of the fluctuation from the one-dimensional region to the three-dimensional region is described. The transition temperatures are given by the bare couplings at high temperatures.     

Anisotropy of Electrical Resistivity and Hole Mobility in InTe Single Crystals

The temperature dependences of the electrical resistivity and Hall mobility of p-type InTe chain single crystals in parallel and perpendicular directions to c-axis have been investigated in the temperature range of 28–260 K. The high anisotropy between ∂‖ and ∂⟂ which depends on temperature is attributed to high concentration of stacking faults due to weak interchain bonding. The mobility parallel to c-axis was found to vary with temperature asμ α Tⁿ where n = -0.6 due to hole scattering on polar optical phonons. The mobility perpendicular to c-axis above 140 K increases with temperature exponentially with an activation energy of 0.03 eV which is attributed to the hopping mechanism due to the barriers between the chains.     

Semiconducting TiO2SiO2 glasses (I): Electronic conductivity

Semiconducting glasses, 70% TiO₂-30% SiO₂, with a Ti³⁺ content varying from zero to 7.8%, have been prepared by rf sputtering in argon/oxygen/hydrogen gas mixtures. Conduction in the Ti³⁺-containing glasses is by small polarons hopping adiabatically. The disorder energy is small (0.05 eV) compared to the hopping energy (0.37–0.51 eV). The variation of the hopping energy with Ti³⁺ content and temperature is ascribed to a polaron overlap effect and to effects arising from the random glass structure, respectively. At low temperatures conduction is a percolation process. The conduction in Ti³⁺-free glasses is not due to polarons; at low temperature these glasses exhibit variable-range hopping.     

The Role of Polymer Cations in The Polymerization and Electrical Conductivity of Polycarbazole

Abstract

The high electrical conductivities (lohm^?1cm^?1) in 3,3’ polycarbazole charge transfer complexes originate from hopping of radical cations delocalized over only two carbazole units. Although some intramolecular transport must occur a significant intermolecular hopping component must be present. In fact there is significant evidence from model compound studies that distinct bound states exist between radical cations on adjacent chains. The radical cations in the N-methyl substituted polymers are so stable that the conductivity remains unchanged for months in air. These same radical cations can propagate a polymerization reaction through exposed chain ends in molten iodine or bromine solvents. Polymerizations, charge transfer doping, solvent casting thus can be carried out by simply dissolving monomer in the molten halogen. The polymerizing liquid iodine solutions can be reduced by S₂O⁴,⁼ to produce neutral polymer.     

Electronic conductivity and structural chemistry in Li-Te-V oxide glasses

The electronic conductivity of the Li₂O-Te₂V₂O₉ glass system reveals that, even for high lithium content, electron hopping occurs between V⁴⁺ and V⁵⁺. The study of the V⁴⁺ content versus various syntheses shows that more than lithium content, the nature of the counter ion used in Li⁺ reagent and its decomposition behavior are responsible for the efficiency of the spontaneous V⁵⁺ reduction via a ‘sprouting’ phenomenon. The electron hopping process implies interconnection of VO_n polyhedra which are accessible for both V⁴⁺ and V⁵⁺ species. Such fact gives information about short and medium range ordering in the glasses. On the basis of the LiVTeO₅ crystal structure and in agreement with wide angle X-ray scattering experiments, a possible rearrangement bringing together VO₅ square pyramids is proposed to explain the electron hopping. Such proposal corresponds to a lithium network forming effect. It could explain why for Li/V>1 the electronic conductivity increases with lithium content while the V⁴⁺ amount remains low.     

Structural and Electrical Properties of Cd Doped InSe Thin Films

Polycrystalline Cd doped InSe thin films were obtained by thermal co‐evaporation of alpha‐In₂Se₃ lumps and Cd onto glass substrates at a temperature of 150°C. The films were annealed at 150°C and 200°C. The films were found to contain around 46% In, 47% Se and 7% Cd in weight. The films exhibited p‐type conductivity. The results of conductivity measurements have revealed that thermionic emission and variable range hopping are the two dominant conduction mechanisms, in the temperature ranges of 320‐160 K and 150‐40 K respectively. It was observed that above 240 K mobility is limited by the scattering at the grain boundaries. As the temperature decreases, thermal lattice scattering followed by the ionized impurity scattering dominate as the two main mechanisms controlling the mobility. Acceptor to donor concentration ratio was found to be slightly increasing due to annealing.     

Spectroscopy of Charge Transfer Complexes of Aniline Blue

Charge transfer (CT) complexes of aniline blue (AB) were prepared with standard organic acceptors such as TCNQ, TCNE, DDQ, and chloranil and studied with UV-VIS-NIR spectra showing σ→π* and π→π* transitions along with free-carrier absorption due to scattering of light particles which has been found involving phonon–photon, electron–photon, and electron–electron scattering. Infrared spectra contain half power beta density due to hopping conduction and an asymmetric band corresponding to A(k) = A₀k exp(?bk) as absorption associated with diffraction of IR light from the crystalline particles.     

Soliton excitations in liquid crystal polyacetylene

Abstract

A disubstituted polyacetylene with lyotropic liquid crystallinity showing SmA was synthesized. The number-average-molecular weight of the polymer was 5.2?×?10⁵ g/mol. Vapor phase iodine doping for the disubstituted polyacetylene in the form of liquid crystal order allows the generation of charge carriers. The ESR measurements show the charge carriers exhibit Pauli paramagnetism, indicating that these carriers are polarons. Mott-type variable range hopping (VRH) conduction of the polymer was observed. The combination of SmA molecular architecture and electrical conduction by polyene as a molecular wire in the polyacetylene derivative results in liquid crystal electrical conduction via electro-soliton movement.     

Electronic and Ionic Conductivity in Polyiodine Complexes of Benzophenones and Coumarin

Abstract

Complexes of benzophenone, benzophenone derivatives, or coumarin with alkali or ammonium iodides and iodine have been prepared and their conductivities studied. The organic sub-lattices involve six- or four-coordinate cation clathrated by the carbonyl compounds. The iodine sub-lattices consist of I_n chains in which I₃ ^? and I₅ ^? ions can be identified. AC (1 KHz) conductivities at room temperature vary from 10^?1 to 10^?6 Ω^?1 cm^?1, and are of a mixed ionic and electronic type. The most likely transport mechanism involves hopping processes in the polyiodine sub-lattice.     

Theoretical Investigation of Impurities and Intercain Coupling in Polyacetylene

In this work we study the efect of the interchain coupling on the electronic density of states in polyacetylene. First we show that a localized interchain coupling can be simulated by a single substitutional impurity scattering and introduces four symmetrical bound levels at the band edges. We then study the evolution of these levels in the presence of a soliton on the chains. Finally we consder a two- dimensional distribution of interchain interwactions and study its effect on the broadening of the band edges. It is found that, when this coupling is taken into acount, the semi conductormetal transition found in charged soliton-Lattices may occur at a concentration of solitons c ～ 5%.     

Density of States in TTF-TCNQ Measured by Inelastic Neutron Scattering

Abstract

The scattering law ζ(ω) of TTF—TCNQ at 77K has been measured between 35 and 455 meV (280-3670cm^?1) by inelastic neutron scattering. The data have been corrected for background then deconvoluted by a resolution function established for the spectrometer INI-B (I.L.L.) and for a powder sample. They are finally compared to the infrared and Raman measurements available.     

Investigation of triple spin correlations and spin dynamics in ferromagnets

Data on the experimental detection and use of three-particle (chiral) spin dynamic correlations in ferromagnets are presented. The oblique-geometry method for investigating polarized neutron small-angle scattering is described, which gives the dependence that the scattering asymmetry has on the polarization P signs and the scattering angle θ. The following results of the dynamics investigation in the critical and ferromagnetic phases in the magnetic field are presented: the temperature dependence of the critical field H _c, the factorization of the momentum transfer dependence of three-particle vertices, the corroboration of the “hard” version of the dipole critical dynamics, and the dynamics of amorphous magnets and invars.     

Optical Field Induced Scattering in Polymer Dispersed Liquid Crystal Films

Abstract

Polymer dispersed liquid crystals are composite materials consisting of inclusions of liquid crystalline materials dispersed in a polymer binder. If the refractive indices of the constituent liquid crystal and polymer are appropriately matched, then films of these materials may be switched between an optically scattering state and a non–scattering transparent state^1?2 by the application of electric fields which reorient the liquid crystal in the inclusions. In this paper we discuss the response of these materials to intense laser radiation, and examine the mechanisms associated with optical field induced reorientation.     

Raman Scattering from Liquid Crystals

Abstract

The use of Raman scattering technique as a tool for studying local order in complex liquid crystal systems is illustrated by three examples, namely the locally anisotropic liquid L-phase, lipid membranes, and PDLC's.     

DC electrical conduction in tungsten phosphate glasses

The dc conductivity of semiconducting tungsten phosphate glasses of three different compositions has been measured over a temperature range 100–400 K. The data have been analysed in the light of existing models of polaronic hopping conduction. The high-temperature region can be qualitatively explained by small-polaron hopping between nearest neighbours, while at low temperatures (below 150 K), the behaviour can be explained by Mott's variable-range hopping. The value of the electron decay constant α estimated from variable-range hopping is of the order of 2 Å^?1, but the estimated disorder energy W_D is twice as large as the measured low-temperature activation energy.     

Compact Permanent Magnetic Circuit with Periodic Magnetic Field Designed for Studies of Liquid Crystals

Abstract

We have developed a high-performance compact magnetic circuit to investigate orientational phase behaviors of biological and synthetic macromolecular systems by using spectroscopic methods such as X-ray scattering and light scattering. This magnetic circuit can apply a periodic magnetic field and gradient to samples. The maximum values of the magnetic field strength and gradient are varied from 1.5 tesla to 0.55 tesla and from 2.4 × 10² tesla/m to 7.3 × 10¹ tesla/m. Owing to the high periodicity of the magnetic field strength and gradient macromolecules are subjected to both rotational and translational forces from the magnetic field. We show some prominent features of this magnetic circuit and its first application to the synchrotron radiation small-angle X-ray scattering (SR-SAXS) studies of supermacromolecular liquid crystals.     

Advanced in Development IR Modulators of Ferroelectric Liquid Crystals Utilizing Transient Light Scattering Effects

Abstract

The highly efficient IR-modulation has been achieved using LC electro-optic elements. Experimental infrared modulator elements have been fabricated and demonstrated utilizing the transient light scattering effect of ferroelectric liquid crystal with asymmetric waveform voltage drive. The new elements performed 80%, 50%, 40% and 25% modulation degree in the 632.8nm, 2, 3-5 and 8-12 μm region. And we observed micro domain structure under the scattering state by a polarizing microscope to understand the mechanism of the domain switching. In addition, we evaluated properties of the scattering angular and temperature dependence quite important for the design of optics for the application in the infrared range.     

Quasielastic Light Scattering from Orientational Fluctuations in a Cholesteric Liquid Crystal

Abstract

Examination of the Rayleigh line of a lyotropic cholesteric polypeptide liquid crystal by the techniques of quasielastic light scattering spectroscopy reveals the presence of two new purely dissipative low frequency light scattering modes of comparable intensity. Angular and electric field dependences of the deconvoluted spectra are consistent with the identification of the mechanism as due to twist and viscous-splay normal modes recently predicted theoretically. Analysis of the narrow mode on this basis yields a value of γ₁, the twist viscosity coefficient of the medium. The broader mode results in an estimate of the value of the ratio of the splay to bend elastic moduli, K ₁₁/K ₃₃ ～ 10^?5, which is shown to be in accord weith mean field theoretical calculations for a system of such highly elongated macromolecules.     

Influence of photonic excitations on the electrical parameters of TlInS2 crystals

The photo‐excitation effect on the current transport mechanism in TlInS₂ crystals has been studied by means of dark and illuminated conductivity measurements. The temperature‐dependent electrical conductivity analysis in the temperature region of 110‐340 K revealed the domination of the thermionic emission and the thermally assisted variable range hopping (VRH) of charge carriers above and below 160 K, respectively. Above 160 K, the conductivity activation energies in the dark are found to be 0.28 and 0.15 eV in the temperature regions of 340‐240 K and 230‐160 K, respectively. In the temperature region of 110‐150 K, the dark variable range hopping analysis revealed a density of localized states of 1.99×10²² cm^–3eV^–1, an average hopping distance of 0.53 nm and an average hopping energy of 79.65 meV. When the sample was photo‐excited, the values of the conductivity activation energies, the density of localized states near the Fermi level and the average hopping energy were observed to decrease sharply with increasing illumination intensity. On the other hand, the average hopping distance increased with rising illumination intensity. Such behaviours were attributed to the Fermi level shift and/or trap density reduction by electron‐hole recombination. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)