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: We present a comprehensive analysis of the optical constants of the two-dimensional dichalcogenide materials 2H-TaSe2 and 2H-NbSe2, in an attempt to address the physics of two-dimensional correlated systems. The title compounds were studied over several decades in frequency, from the far-infrared to the ultraviolet. Measurements with linearly polarized light have allowed us to obtain both the in-plane and out-of-plane components of the conductivity tensor. Although the electromagnetic response of dichalcogenides is strongly anisotropic, both the in-plane and out-of-plane components of the conductivity tensor share many common features, including the presence of a well-defined metallic component, as well as a “mid-infrared band”. We discuss the implications of these results in the context of the spectroscopic results of other classes of low-dimensional conductors such as the high-temperature superconducting cuprates. In particular, the analysis of the redistribution of the spectral weight as a function of temperature, as well as the behavior of the quasiparticles relaxation rate, points to significant distinctions between the charge dynamics of dichalcogenides and other classes of low dimensional conductors. [ABSTRACT FROM AUTHOR]

We present the results of a dc transport and optical investigation of WO3 and NaxWO3 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. [ABSTRACT FROM AUTHOR]

This paper illustrates the complete dynamics of the laminar-turbulent transition process in a plasma plume using a simple measurement of the magnation-point heat flux correlated with acoustic, optical, and voltage drop fluctuations. In the laminar flow regime a steady jet is produced and the heat fluxes are accurately predicted hr laminar correlations. The initial stage of transition is characterized by the formation of axisymmetric structures and velocity fluctuations which increase the heat flux over laminar correlations. This is followed by a rapid decrease in heat flux as the vortex structures become more intense and rapidly entrain external air into the plume. The plume oscillations (acoustical and voltage drop) become most intense and are identical in frequency at the point of minimum heat flux. The transition is complete which the transition to small-scale turbulence in the exiting boundary layer which results in dec reased entrainment and increased heat flux. [ABSTRACT FROM AUTHOR]

The design criteria used in the development of IR station 13.3 at the Daresbury SRS are reviewed particularly in terms of its principle application to reflection-absorption infrared spectroscopy (RAIRS). An example of current performance is given in the form of a RAIR spectrum of chlorine atoms adsorbed on Ag (100). The application of the station to infrared microscopy is reviewed and IR spectra from a thin polymer laminate are used to compare performance with that using a conventional infrared source. [ABSTRACT FROM AUTHOR]

The optical reflectivity as a function of temperature of the title compound for x =0, 5 and 12 has been measured over a broad spectral range from 4 meV up to 12 eV. Our findings suggest a very anisotropic dynamics of the charge excitation spectrum when measuring along or perpendicular to the ladders. Moreover, a metal-insulator transition develops at low temperatures, leading to a suppression of Drude spectral weight in the far and mid-infrared spectral range. We identify this behaviour as a consequence of the localization effects for small Ca substitution, and of the possible formation of a charge density wave condensate for large Ca substitution. [ABSTRACT FROM AUTHOR]

By comparing the optical conductivities of La1.67Sr0.33NiO4 (LSNO), Sr1.5La0.5MnO4 (SLMO), Nd2CuO4-y (NCO), and Nd1.96Ce0.04CuO4 (NCCO), we have identified a peculiar behavior of polarons in this cuprate family. Whereas in LSNO and SLMO small polarons localize into ordered structures below a transition temperature, in these cuprates the polarons appear to be large, and at low T their binding energy decreases. This reflects an increase of the polaron radius, which may trigger coherent transport. [ABSTRACT FROM AUTHOR]