The normal state scattering rate in high- cuprates

A detailed phenomenological model is developed for the normal state transport properties of optimal and overdoped high-T_c cuprates. In particular, an explicit form of scattering rate is identified that may account, qualitatively and quantitatively, for the normal state (magneto)-transport properties of Tl₂Ba₂CuO _{6 + δ} and Bi₂Sr₂CaCu₂O _{8 + δ} across the overdoped side of the phase diagram. The proscribed form of the scattering rate is consistent also with features seen in the photoemission spectroscopy of Bi₂Sr₂CaCu₂O _{8 + δ} and offers a new and intuitive way to understand the evolution of the temperature dependence of the inverse Hall angle in Bi-based cuprates with carrier concentration. Received 5 June 2002 / Received in final form 17 December 2002 Published online 6 March 2003 RID="a" ID="a"e-mail: n.e.hussey@bristol.ac.uk     

Quasiparticle relaxation in Heavy Fermions studied using Inverse Fourier Transform of optical conductivity

Inverse Fourier Transform of optical conductivity is used for studies of quasiparticle relaxation in Heavy Fermions in time domain. We demonstrate the usefulness of the procedure on model spectra and then use it to study quasiparticle relaxation in two Heavy Fermions YbFe₄Sb₁₂ and CeRu₄Sb₁₂. Optical conductivity in time domain reveals details of quasiparticle relaxation close to the Fermi level, not readily accessible from the spectra in the frequency domain. In particular, we find that the relaxation of heavy quasiparticles does not start instantaneously, but typically after a few hundred femto-seconds.     

Spin-fluctuation gating in the c-axis non-Drude conductivity of the high Tc cuprates

An ideal antiferromagnetic (AF) ordering of the spins of the CuO layers of an underdoped cuprate prevents the low energy tunneling of the charge carriers between the layers. In order to obtain a non-vanishing c-axis conductivity (σ_c), we invoke ground state fluctuations of the spin system. These provide a frequency-dependent gating effect by changing the direction of the AF order parameter within one layer relative to that in a neighboring layer, thereby permitting some tunneling. The calculated σ_c compares favorably with experimental data in a) being small and b) having a weak frequency dependence of distinctly non-Drude form.     

Transport and optical conductivity in

We present the results of a dc transport and optical investigation of WO₃ and Na_xWO₃ with x =0.01. Upon Na-doping we find a (Drude) metallic component in the optical conductivity, while the transport data display a crossover from an activated to a variable range hopping regime around 210 K. We suggest the possible formation of polarons (and bipolarons) and speculate that superconductivity could be induced, provided the dc percolation threshold is achieved. Received 28 March 2000     

The study of optical parameters and DC conductivity of Se100−xHgx thin films

Se_100−xHg_x bulk samples have been prepared by conventional melt quenching technique. The thin films of the material have been prepared on glass substrate using the thermal evaporation technique. The transmission spectra has been studied to measure the optical constants like absorption coefficient (α), extinction coefficient (K), optical band gap (E_g), Urbach energy (E_e). The DC conductivity (σ_dc) of Se_100−xHg_x has been also studied to find the activation energy (ΔE_a)$(\mathrm{\Delta }{E}_a)$. The optical band gap increases and Urbach energy first increases then decreases with increase in Hg concentration. DC conductivity and activation energy increases with increase in Hg concentration. These materials are found suitable for the optical disk materials and in optoelectronic devices due to their high absorption coefficient and dependence of reflectance on composition.     

Remarkable enhancement of terahertz conductivity of graphene tuned by periodic gate voltage

Optical conductivity of a graphene sheet subject to a one-dimensional cosinusoidal potential is studied. We find that the optical conductivity can be tuned by the strength of the superlattice potential. When this strength is within a certain range the terahertz conductivity can be enhanced by two orders of magnitude.     

Progress in the understanding of the normal state of the cuprates

Over the last years there has been increasing evidence that the normal state of the cuprates can not be described adequately with individual quasiparticles within Fermi-liquid theory. While the low-lying excitations in the superconducting state are nevertheless possibly of quasiparticle character, this character vanishes with the loss of superconducting phase coherence when going to the normal conducting state. Generally, this normal state is characterized by strong heterogeneity. In real space this manifests in charge and spin ordering, either static or dynamical, the so-called ‘stripes’. The spectral signatures of various models describing this unusual metallic normal state together with less exotic non-Fermi-liquid models, like the marginal Fermi liquid, will be compared to photoemission spectra with high angular and energy resolution and to results obtained by other methods. Received: 19 March 2002 / Accepted: 2 October 2002 / Published online: 5 February 2003 RID="*" ID="*"Corresponding author. Fax: +49-30/2093-7729, E-mail: christoph.janowitz@physik.hu-berlin.de     

Peculiarity of charge dynamics in High-Tc cuprates

Discussion is focused on the peculiarity of the out-of-plane and the in-plane charge dynamics related to the two-dimensionality in high-T_c cuprates. Recent observations of a double Josephson plasmon and a intra-bilayer Josephson effect remind us that each CuO₂-plane is in fact an independent superconducting layer, suggesting that the superconducting coherence length in the c-direction is shorter than the interlayer distance. The origin of this extremely short c-axis coherence length as well as the long c-axis penetration depth is discussed in relation with the incoherent c-axis transport in the normal state. Another peculiarity is a strong itinerant nature of charges within the planes. As an example, it is demonstrated that a static charge order is inhibited even in the “stripe” phase in the cuprates.     

Electrical conductivity and optical transparency of bacterial cellulose based composite by static and agitated methods

Composites consisting of bacterial cellulose (BC) and ionic conducting polymer (ICP) were prepared. BC was biosynthesized in media at 0, 25, 50 and 100 rpm. ICP was chemically synthesized at different concentrations of ionic salt. The corresponding electrical conductivity of the composites was measured as a function of ionic salt concentration. ICP improved the optical transparency and electrical conductivity of the BC/ICP composites. Morphological images of BC/ICP composites showed that the pore size of the BC pellicle increased while the diameter and density of the BC fibers decreased. The cultivation method was critical in affecting the structure and electrical conductivity of the composites.     

光学塑料开发的历史与现状

本文简要回顾了光学塑料研制、应用的历史，叙述了国内外光学塑料开发、应用的现状及最新动态，分析了光学塑料的市场需求和开发前景。     

Electric and magnetic field modulated energy dispersion,conductivity and optical response in double quantum wire with spin-orbit interactions

We study the influence of electric field on the electronic energy band structure, zero-temperature ballistic conductivity and optical properties of double quantum wire. System described by double-well anharmonic confinement potential is exposed to a perpendicular magnetic field and Rashba and Dresselhaus spin-orbit interactions. Numerical results show up that the combined effects of internal and external agents cause the formation of crossing, anticrossing, camel-back/anomaly structures and the lateral, downward/upward shifts in the energy dispersion. The anomalies in the energy subbands give rise to the oscillation patterns in the ballistic conductance, and the energy shifts bring about the shift in the peak positions of optical absorption coefficients and refractive index changes.     

Drude Weight, Optical Conductivity of Two-Dimensional Hubbard Model at Half Filling

We study the Drude weight D and optical conductivity of the two-dimensional （2D） Hubbard model at half filling with staggered magnetic flux （SMF）. When SMF being introduced, the hopping integrals are modulated by the magnetic flux. The optical sum rule, which is related to the mean kinetic energy of band electrons, is evaluated for this 2D Hubbard Hamiltonian. Our present result gives the dependence of the kinetic energy, D and the optical conductivity on SMF and U. At half filling D vanishes exponentially with system size. We also find in the frequency dependence of the optical conductivity, there is δ-function peak at ω ≈ 2｜m｜U and the incoherent excitations begin to present themselves extended to a higher energy region.     

Method of state code matrixes in the realization of optical switching using Perfect Shuffle

Based on the Left Perfect Shuffle (LPS) optical communication network constructed by cascade multi-stage LPS interconnection, using Looping algorithm, any arbitrary sequence of the input signals can be realized. However, instead of obtaining the simultaneous state codes of the same level node switches through mathematical analytical expressions directly, only routing tags of each channel can be obtained through mathematical analytical expressions so as to draw out topological chart of the network to obtain the state codes implied in the chart. Thus, the states of the switches cannot be directly programmed and controlled by computer in practical application. In this paper, based on the Looping algorithm, a method of stage code matrixes is presented to resolve this problem. By using the method, the simultaneous state codes of the same level’s four node switches can be directly obtained, which is convenient for the computer to provide controlled signals needed to finish the permutation for each node switch. The method of stage code matrixes provides further theoretical basis for the realization of optical switching by integration of Perfect Shuffle and high-speed optical switches.     

Investigations on the effect of complexation of NaF salt with polymer blend (PEO/PVP) electrolytes on ionic conductivity and optical energy band gaps

Sodium ion conducting polymer blend electrolyte films, based on polyethylene oxide (PEO) and polyvinyl pyrrolidone (PVP) complexed with NaF salt, were prepared using solution casting technique. The complexation of the salt with the polymer blend was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and UV-vis spectroscopy. Electrical conductivity of the films was measured with impedance analyzer in the frequency range of 1 Hz to 1 MHz and in the temperature range of 303-348 K. It was observed that the magnitude of conductivity increased with the increase in the salt concentration as well as the temperature. UV-vis absorption spectra in wavelength region of 200-800 nm were used to evaluate the optical properties like direct and indirect optical energy band gaps, optical absorption edge. The optical band gaps decreased with the increase in Na⁺ ion concentration. This suggests that NaF, as a dopant, is a good choice to improve the electrical properties of PEO/PVP polymer blend electrolytes.     

Quantum state sharing using linear optical elements

Motivated by protocols [G. Gordon, G. Rigolin, Phys. Rev. A 73 (2006) 062316] and [N.B. An, G. Mahler, Phys. Lett. A 365 (2007) 70], we propose a linear optical protocol for quantum state sharing of polarization entangled state in terms optical elements. Our protocol can realize a near-complete quantum state sharing of polarization entangled state with arbitrary coefficients, and it is possible to achieve unity fidelity transfer of the state if the parties collaborate. This protocol can also be generalized to the multi-party system.     

Monte Carlo simulation of electric conductivity for pure and doping fullerene (C60)

In this paper, we have used Monte Carlo (MC) method to simulate and study the temperature and doping effects on the electric conductivity of fullerene (C60). The results show that the band gap has reduced by the doping and the charge carrier transport is facilitated from valence band to conduction band by the temperature where is touched a 300 K. In this case, the conductivity reached a value of $4\times {10}^{-7}\text{S}{\text{cm}}^{-1}$. The electric conductivity of C60 can increase by the triphenylmethane dye crystal violet (CV) alkali metal to reach $4\times {10}^{-3}\text{S}{\text{cm}}^{-1}$ at 303 K. Our results of MC simulation have a good agreement with those extracted from literature [10], [33].     

Nernst effect and disorder in the normal state of high-T(c) cuprates

We have studied the influence of disorder induced by electron irradiation on the Nernst effect in optimally and underdoped YBa2Cu3O(7-delta) single crystals. The fluctuation regime above T(c) expands significantly with disorder, indicating that the T(c) decrease is partly due to the induced loss of phase coherence. In pure crystals the temperature extension of the Nernst signal is found to be narrow whatever the hole doping, contrary to data reported in the low-T(c) cuprate families. Our results show that the presence of intrinsic disorder can explain the enhanced range of the Nernst signal found in the pseudogap phase of the latter compounds.