Optical investigation of the metal-insulator transition in FeSb2FeSb_2

We present a comprehensive optical study of the narrow gap $FeSb_2$ semiconductor. From the optical reflectivity, measured from the far infrared up to the ultraviolet spectral range, we extract the complete absorption spectrum, represented by the real part $\sigma_1(\omega)$ of the complex optical conductivity. With decreasing temperature below 80 K, we find a progressive depletion of $\sigma_1(\omega)$ below $E_g\sim 280$ cm$^{-1}$, the semiconducting optical gap. The suppressed (Drude) spectral weight within the gap is transferred at energies $\omega>E_g$ and also partially piles up over a continuum of excitations extending in the spectral range between zero and $E_g$. Moreover, the interaction of one phonon mode with this continuum leads to an asymmetric phonon shape. Even though several analogies between $FeSb_2$ and $FeSi$ were claimed and a Kondo-insulator scenario was also invoked for both systems, our data on $FeSb_2$ differ in several aspects from those of $FeSi$. The relevance of our findings with respect to the Kondo insulator description will be addressed.Comment: 17 pages, 5 figure

Anisotropy in the magnetic and electrical transport properties of Fe1-xCrxSb2

We have investigated anisotropy in magnetic and electrical transport properties of Fe1-xCrxSb2 (0<= x <=1) single crystals. The magnetic ground state of the system evolves from paramagnetic to antiferromagnetic with gradual substitution of Fe with Cr. Anisotropy in electrical transport diminishes with increased Cr substitution and fades away by x=0.5. We find that the variable range hopping (VRH) conduction mechanism dominates at low temperatures for 0.4<= x <=0.75.Comment: 5 pages, 6 figure

Comparison of stray-light and diffraction-caused crosstalk in free-space optical interconnects

In this paper we investigate for the first time the effect of the crosstalk introduced due to laser beam imaging in a free-space optical interconnect (FSOI) system. Due to the overfill of the transmitter microlens array by the vertical cavity surface emitting laser (VCSEL) beam, one part of the signal is imaged by the adjacent microlens to another channel, possibly far from the intended one. Even though this causes increase in interchannel and intersymbol interference, to our knowledge this issue has been neglected so far. The numerical simulation has been performed using a combination of exact ray tracing and the beam propagation methods. The results show that some characteristics of stray-light crosstalk are similar to that of diffraction-caused crosstalk, where it is strongly dependent on the fill factor of the microlens, array pitch, and the channel density of the system. Despite the similarities, the stray-light crosstalk does not affect by an increase in the interconnection distance. As simulation models for optical crosstalk are numerically intensive, we propose here a crosstalk behavioural model as a useful tool for optimisation and design of FSOIs. We show that this simple model compares favourably with the numerical simulation models

Nanofabricated media with negative permeability at visible frequencies

We report a nanofabricated medium made of electromagnetically coupled pairs of gold dots with geometry carefully designed at a 10-nm level. The medium exhibits strong magnetic response at visible-light frequencies, including bands with negative \mu. The magnetism arises due to the excitation of quadrupole plasmon resonances. Our approach shows for the first time the feasibility of magnetism at optical frequencies and paves a way towards magnetic and left-handed components for visible optics.Comment: 16 pages, 4 figures. submitted to Nature on 1 April 200

Effect of aging on mechanical properties of Al-8Si-8Fe-1.4V/SiCp composites

In this study, Al-8Fe-8Si-1.4V/SiCp composites fabricated by squeeze casting process were age-hardened to study the influence of heat treatment on mechanical properties, such as hardness, bending strength and modulus of elasticity. The cast samples were solid sоluted at 540 °C for one hour, then quenched in water to room temperature, and finally aged at 190 °C for 2, 4, 6, 8 and 10 hours for hardness test and at 195 °C for 2, 6 and 10 hours for bending strength determination

Soil-structure interaction assessment combining deconvolution of building and field recordings with polarization analysis: application to the Matera (Italy) experiment

In this study, the wavefield radiated from a building to its surroundings is identified and extracted from M4.6 earthquake recordings collected by sensors installed in a building and on the nearby athletic field in Matera (Italy) using a new approach for soil-structure interaction assessment. The proposed approach for earthquake data analysis combines in an innovative way two methods already used in seismology and engineering seismology: deconvolution and polarization analysis. The approach enables the identification, reconstruction, and characterization of the wavefield radiated from a vibrating building into its surroundings, and the estimation of the amount of energy associated with it. The approach consists of four steps: (1) estimation of the resonant frequencies of the building, (2) deconvolution of the earthquake recordings from a building and its surroundings, (3) identification of the seismic phases, reconstruction of the signal transmitted from the building to its surroundings, and estimation of its energy, and (4) polarization analysis. Analysis of recordings of the M4.6 event highlighted that the motion related to the wavefield radiated from the building to the ground was mostly linearly polarized in the radial and transverse planes, while a clear ellipticity was observed only in the horizontal plane. The wavefield radiated from the building might be dominated by unconventionally polarized surface waves, i.e., quasi-Rayleigh waves or a combination of quasi-Rayleigh and quasi-Love waves. The results indicated that the energy transmitted from the analyzed vibrating building to its surroundings was significant and decreased the ground motion shaking due to the out-of-phase motion

The Effect of the Higher Order Modes on the Optical Crosstalk in Free-Space Optical Interconnect

In this paper we investigate the effect of the crosstalk introduced due to laser beam imaging in a free-space optical interconnect (FSOI) system. Due to the overfill of the transmitter microlens array by the vertical-cavity surface-emitting laser (VCSEL) beam, one part of the signal is imaged by the adjacent microlens to another channel, possibly far from the intended one. Furthermore, it is known that in practice, VCSELs tend to operate in several transverse modes simultaneously. This will cause even more increase in the interchannel and intersymbol interference, to our knowledge this issue has been neglected so far. The numerical simulation has been performed using a combination of exact ray tracing and the beam propagation methods. The results show that the stray-light crosstalk will increase significantly with either greater system density or higher order modes. The diffraction-caused crosstalk is mainly affected primarily by interconnection distance, channel density

Nonvanishing Energy Scales at the Quantum Critical Point of CeCoIn5

Heat and charge transport were used to probe the magnetic field-tuned quantum critical point in the heavy-fermion metal CeCoIn$_5$. A comparison of electrical and thermal resistivities reveals three characteristic energy scales. A Fermi-liquid regime is observed below $T_{FL}$, with both transport coefficients diverging in parallel and $T_{FL}\to 0$ as $H\to H_c$, the critical field. The characteristic temperature of antiferromagnetic spin fluctuations, $T_{SF}$, is tuned to a minimum but {\it finite} value at $H_c$, which coincides with the end of the $T$-linear regime in the electrical resistivity. A third temperature scale, $T_{QP}$, signals the formation of quasiparticles, as fermions of charge $e$ obeying the Wiedemann-Franz law. Unlike $T_{FL}$, it remains finite at $H_c$, so that the integrity of quasiparticles is preserved, even though the standard signature of Fermi-liquid theory fails.Comment: 4 pages, 4 figures (published version