Observation of thermally activated glassiness and memory dip in a-NbSi insulating thin films

We present electrical conductance measurements on amorphous NbSi insulating thin films. These films display out-of equilibrium electronic features that are markedly different from what has been reported so far in disordered insulators. Like in the most studied systems (indium oxide and granular Al films), a slow relaxation of the conductance is observed after a quench to liquid helium temperature which gives rise to the growth of a memory dip in MOSFET devices. But unlike in these systems, this memory dip and the related conductance relaxations are still visible up to room temperature, with clear signatures of a temperature dependent dynamics

Dark energy with non-adiabatic sound speed: initial conditions and detectability

Assuming that the universe contains a dark energy fluid with a constant linear equation of state and a constant sound speed, we study the prospects of detecting dark energy perturbations using CMB data from Planck, cross-correlated with galaxy distribution maps from a survey like LSST. We update previous estimates by carrying a full exploration of the mock data likelihood for key fiducial models. We find that it will only be possible to exclude values of the sound speed very close to zero, while Planck data alone is not powerful enough for achieving any detection, even with lensing extraction. We also discuss the issue of initial conditions for dark energy perturbations in the radiation and matter epochs, generalizing the usual adiabatic conditions to include the sound speed effect. However, for most purposes, the existence of attractor solutions renders the perturbation evolution nearly independent of these initial conditions.Comment: 16 pages, 2 figures, version accepted in JCA

Single-sided CZT strip detectors

We report progress in the study of thick CZT strip detectors for 3-d imaging and spectroscopy and discuss two approaches to device design. We present the spectroscopic, imaging, detection efficiency and response uniformity performance of prototype devices. Unlike double-sided strip detectors, these devices feature both row and column contacts implemented on the anode surface. This electron-only approach circumvents problems associated with poor hole transport in CZT that normally limit the thickness and energy range of double-sided strip detectors. These devices can achieve similar performance to pixel detectors. The work includes laboratory and simulation studies aimed at developing compact, efficient, detector modules for 0.05 to 1 MeV gamma radiation measurements. The low channel count strip detector approach can significantly reduce the complexity and power requirements of the readout electronics. This is particularly important in space-based coded aperture or Compton telescope instruments requiring large area, large volume detector arrays. Such arrays will be required for NASA\u27s Black Hole Finder Probe (BHFP) and Advanced Compton Telescope (ACT)

Density-based mixing parameter for hybrid functionals

A very popular ab-initio scheme to calculate electronic properties in solids is the use of hybrid functionals in density functional theory (DFT) that mixes a portion of Fock exchange with DFT functionals. In spite of their success, a major problem still remains, related to the use of one single mixing parameter for all materials. Guided by physical arguments that connect the mixing parameter to the dielectric properties of the solid, and ultimately to its band gap, we propose a method to calculate this parameter from the electronic density alone. This method is able to cut significantly the error of traditional hybrid functionals for large and small gap materials, while retaining a good description of structural properties. Moreover, its implementation is simple and leads to a negligible increase of the computational time.Comment: submitte

Study of 5 and 10 mm thick CZT strip detectors

We report progress in the study of 5 and 10 mm thick CZT strip detectors featuring orthogonal coplanar anode contacts. This novel anode geometry combines the advantages of pixel detectors with those of double-sided strip detectors. Like pixel detectors, these are electron-only devices that perform well as hard x-ray and y-ray spectrometers and imagers even in the thicker configurations required for reasonable detection efficiency at 1 MeV. Like double-sided strip detectors in an N x N configuration, these detectors require only 2N readout channels to form N2 “pixels”. Unlike doublesided strip detectors, all signal contacts for spectroscopy and 3- d imaging are formed on one detector surface. Polymer flip chip bonding to a ceramic substrate is employed resulting in a rugged and compact detector assembly. Prototype detector modules 5 mm thick have been fabricated and tested. Prototype modules, 10 mm thick, are currently in procurement. Measurements confirm these devices are efficient detectors throughout their volume. Sub-millimeter position resolution and energy resolution (FWHM) better than 3% at 662 keV and 15% at 60 keV throughout the detector volume are demonstrated. Options for processing the signals from the non-collecting anode strip contacts are discussed. Results from tests of one prototype circuit are presented. We also report on detector simulation studies aimed at defining an optimum geometry for the anode contacts and at determining optimum operating conditions and the requirements of the signal processing electronics

Single-sided CZT strip detectors

We report progress in the study of thick CZT strip detectors for 3-D imaging and spectroscopy and discuss two approaches to device design. Unlike double-sided strip detectors, these devices feature both row and column contacts implemented on the anode surface. This electron-only approach circumvents problems associated with poor hole transport in CZT that normally limit the thickness and energy range of double-sided strip detectors. The work includes laboratory and simulation studies aimed at developing compact, efficient, detector modules for 0.05 to 1 MeV gamma radiation measurements while minimizing the number and complexity of the electronic readout channels. These devices can achieve similar performance to pixel detectors for both 3-D imaging and spectroscopy. The low channel count approach can significantly reduce the complexity and power requirements of the readout electronics. This is particularly important in applications requiring large area detector arrays. We show two single-sided strip detector concepts. One, previously reported, features rows established with collecting contacts and columns with noncollecting contacts. Another, introduced here, operates on a charge sharing principle and establishes both rows and columns with collecting contacts on the anode surface. In previous work using the earlier strip detector concept we reported simulations and measurements of energy and spatial resolution for prototype 5- and 10-mm-thick CZT detectors. We now present the results of detection efficiency and uniformity measurements conducted on 5-mm-thick detectors using a specific configuration of the front-end electronics and event trigger. We discuss the importance of the detector fabrication processes when implementing this approach

Comment on ``Deterministic equations of motion and phase ordering dynamics''

Zheng [Phys. Rev. E {\bf 61}, 153 (2000), cond-mat/9909324] claims that phase ordering dynamics in the microcanonical $\phi^4$ model displays unusual scaling laws. We show here, performing more careful numerical investigations, that Zheng only observed transient dynamics mostly due to the corrections to scaling introduced by lattice effects, and that Ising-like (model A) phase ordering actually takes place at late times. Moreover, we argue that energy conservation manifests itself in different corrections to scaling.Comment: 5 pages, 4 figure

Readout and performance of thick CZT strip detectors with orthogonal coplanar anodes

We report progress in the study of CZT strip detectors featuring orthogonal coplanar anode contacts. The work includes laboratory and simulation studies aimed at optimizing and developing compact, efficient, high performance detector modules for 0.05 to 1 MeV gamma radiation measurements. The novel coplanar anode strip configuration retains many of the performance advantages of pixel detectors yet requires far fewer electronic channels to perform both 3-d imaging and spectroscopy. We report on studies aimed at determining an optimum configuration of the analog signal processing electronics to employ with these detectors. We report measurements of energy and spatial resolution in three dimensions for prototype 5 and 10 mm thick CZT detectors using a set of shaping and summing amplifiers

Development of CZT strip detector modules for 0.05- to 1-MeV gamma-ray imaging and spectroscopy

We report progress in our study of cadmium zinc telluride (CZT) strip detectors featuring orthogonal coplanar anode contacts. We specifically report on the performance, characterization and stability of 5 and 10 mm thick prototype CZT detectors fabricated using material from several manufacturers. Our ongoing work includes laboratory and simulation studies aimed at optimizing and developing compact, efficient, high performance detector modules for 0.05 to 1 MeV gamma radiation measurements with space-based instrumentation. The coplanar anode strip configuration retains many of the performance advantages of pixel detectors yet requires far fewer electronic channels to perform both 3-d imaging and spectroscopy. Minimizing the channel count is important for large balloon or space instruments including coded aperture telescopes (such as MARGIE or EXIST) and Compton imaging telescopes (such as TIGRE or ACT). We also present plans for developing compact, space qualified imaging modules designed for integration into closely packed large area detector arrays. We discuss issues associated with detector module and array electronics design and development

Generation of two-color polarization-entangled optical beams with a self-phase-locked two-crystal Optical Parametric Oscillator

A new device to generate polarization-entangled light in the continuous variable regime is introduced. It consists of an Optical Parametric Oscillator with two type-II phase-matched non-linear crystals orthogonally oriented, associated with birefringent elements for adjustable linear coupling. We give in this paper a theoretical study of its classical and quantum properties. It is shown that two optical beams with adjustable frequencies and well-defined polarization can be emitted. The Stokes parameters of the two beams are entangled. The principal advantage of this setup is the possibility to directly generate polarization entangled light without the need of mixing four modes on beam splitters as required in current experimental setups. This device opens new directions for the study of light-matter interfaces and generation of multimode non-classical light and higher dimensional phase space