Search results for "CONDUCTIVITY"
showing 10 items of 1988 documents
Emery vs. Hubbard model for cuprate superconductors: A composite operator method study
2013
Within the Composite Operator Method (COM), we report the solution of the Emery model (also known as p-d or three band model), which is relevant for the cuprate high-Tc superconduc- tors. We also discuss the relevance of the often-neglected direct oxygen-oxygen hopping for a more accurate, sometimes unique, description of this class of materials. The benchmark of the solution is performed by comparing our results with the available quantum Monte Carlo ones. Both single- particle and thermodynamic properties of the model are studied in detail. Our solution features a metal-insulator transition at half filling. The resulting metal-insulator phase diagram agrees qual- itatively very well with …
Transition-edge microcalorimeters for X-ray space applications
2000
Abstract In an European Space Agency funded research project, our goal is to develop microbolometer technology for X-ray and far-infrared detection for ESA's future scientific missions. We report results on the X-ray calorimeter, which is based on the superconducting transition of the Ti/Au thermometer strip at about 200 mK. Incident X-rays heat up a Bi absorber, deposited on top of the 400 μm ×400 μm thermometer. The temperature rise of the absorber is measured as a change of the thermometer current with a SQUID operating at 1 K.
Coulomb blockade-based nanothermometry in strong magnetic fields
1998
We have performed experiments to test for the susceptibility to strong magnetic fields of electron tunneling in normal metal -based nanostructures for Coulomb blockade primary thermometry. We have confirmed that, to within our accuracy of about ±1%, the single electron charging -induced zero bias differential resistance maximum is unaffected by the field up to 23 T at temperatures of 0.4–4.2 K. We discuss the simple theoretical basis of this immunity. We also report on the practical limitation at low temperatures imposed by superconductivity of aluminium in small magnetic fields.
Fluctuation-Limited Noise in a Superconducting Transition-Edge Sensor
2003
In order to investigate the origin of the until now unaccounted excess noise and to minimize the uncontrollable phenomena at the transition in x-ray microcalorimeters we have developed superconducting transition-edge sensors into an edgeless geometry, the so-called Corbino disk, with superconducting contacts in the center and at the outer perimeter. The measured rms current noise and its spectral density can be modeled as resistance noise resulting from fluctuations near the equilibrium superconductor-normal metal boundary. Peer reviewed
Spectral broadening by incomplete thermalization of the energy in X-ray microcalorimeters with superconducting absorber and NTD-Ge thermal sensor
2004
Abstract We present a model of the response of a cryogenic microcalorimeter with superconducting absorber and phonon sensitive thermal sensor to the absorption of X-ray photons. The model is based on the main microscopic processes responsible for the thermalization of the deposited energy. We use a system of rate equations to describe the energy downconversion in the superconductor and transport to the thermal sensor. The model is a tool to investigate the thermalization efficiency with respect to the device characteristics (i.e. absorber material, geometry), in order to optimize the performances of these detectors. As a first case study, we report results of simulations for a microcalorime…
Vortex-glass transition in three dimensions.
1991
We investigate the possibility of a vortex-glass transition in a disordered type-II superconductor in a magnetic field in three dimensions by numerical studies of a simplified model. Monte Carlo simulations at finite temperature and domain-wall renormalization-group calculations at {ital T}=0 indicate that {ital d}=3 is just above the lower critical dimension {ital d}{sub {ital l}}, though the possibility that {ital d}{sub {ital l}}=3 cannot be definitely ruled out. A comparison is made with {ital XY} and Ising spin glasses. The (effective) correlation-length exponent {nu} and dynamical exponent {ital z} are in fairly good agreement with experiment.
Phase diagram of dirty two-band superconductors and observability of impurity-induced $s+is$ state
2016
We investigate the phase diagram of dirty two-band superconductors. This paper primarily focuses on the properties and observability of the time-reversal symmetry-breaking $s+is$ superconducting states, which can be generated in two-band superconductors by interband impurity scattering. We show that such states can appear in two distinct ways. First, according to a previously discussed scenario, the $s+is$ state can form as an intermediate phase at the impurity-driven crossover between $s_{\pm}$ and $s_{++}$ states. We show that there is a second scenario where domains of the $s+is$ state exists in the form of an isolated dome inside the $s_{\pm}$ domain, completely detached from the transi…
Numerical investigation of one‐dimensional tunnel junction arrays at temperatures above the Coulomb blockade regime
1996
Arrays of tunnel junctions provide simple thermometric parameters in the limit where thermal excitations dominate over charging effects. We present numerical simulations for calculating the current versus voltage characteristics of an arbitrary one‐dimensional array at arbitrary temperatures on the premise of the ‘‘orthodox theory.’’ The purpose of the computer simulations is to investigate the suitability of tunnel junction arrays for thermometry at low temperatures when the analytical formulas do not hold and, specifically, to see the effect of background charges in this regime.
A mathematical model of counterflow superfluid turbulence describing heat waves and vortex-density waves
2008
The interaction between vortex density waves and high-frequency second sound in counterflow superfluid turbulence is examined, incorporating diffusive and elastic contributions of the vortex tangle. The analysis is based on a set of evolution equations for the energy density, the heat flux, the vortex line density, and the vortex flux, the latter being considered here as an independent variable, in contrast to previous works. The latter feature is crucial in the transition from diffusive to propagative behavior of vortex density perturbations, which is necessary to interpret the details of high-frequency second sound.
Soil ionization in earth electrodes by a finite difference time domain scheme
2004
This paper proposes a finite difference time domain numerical scheme devoted to analyze the transient behavior of earth electrodes during the soil breakdown that can take place when a surge current has to be drained. To this aim, Maxwell's equations together with a space-time variable resistivity function are used. The model has been validated by comparing the computed results with data available in the technical literature. Simulation results related to complex earth electrodes of limited extension are reported. Electrodes of larger extension can be easily simulated but requiring more computational resources.