Search results for "Conductor"
showing 10 items of 1270 documents
Colloquium: Nonequilibrium effects in superconductors with a spin-splitting field
2018
This Colloquium discusses the recent progress in understanding the properties of spin-split superconductors under nonequilibrium conditions. Recent experiments and theories demonstrate a rich variety of transport phenomena occurring in devices based on such materials that suggest direct applications in thermoelectricity, low-dissipative spintronics, radiation detection, and sensing. This text discusses different experimental situations and presents a theoretical framework based on quantum kinetic equations. This framework provides an accurate description of the nonequilibrium distribution of charge, spin, and energy, which are the relevant nonequilibrium modes, in different hybrid structure…
Superconductivity near a magnetic domain wall
2018
We study the equilibrium properties of a ferromagnetic insulator/superconductor structure near a magnetic domain wall. We show how the domain wall size is affected by the superconductivity in such structures. Moreover, we calculate several physical quantities altered due to the magnetic domain wall, such as the spin current density and local density of states, as well as the resulting tunneling conductance into a structure with a magnetic domain wall.
The influence of AlN buffer over the polarity and the nucleation of self-organized GaN nanowires
2015
We experimentally investigate the influence of AlN buffer growth on the nucleation and the polarity of a self-organized assembly of GaN nanowires (NWs) grown on Si. Two complementary growth mechanisms for AlN buffer deposited on Si are demonstrated. Both emphasize the aggregation of Si on the AlN surface and the growth of large cubic crystallites, namely, AlN pedestals. Further growths of GaN NWs assembly reveal that the GaN 2D layer found at the bottom of the NW assembly is the result of the coalescence of Ga-polar pyramids, whereas AlN pedestals are observed as preferential but not exclusive NW nucleation sites. NWs are N-polar or exhibit inversion domains with a Ga-polar core/N-polar she…
Phase segregation in Mg$_{x}$Zn$_{1-x}$O probed by optical absorption and photoluminescence at high pressure
2017
The appearance of segregated wurtzite Mg$_x$Zn$_{1-x}$O with low Mg content in thin films with $x>0.3$ affected by phase separation, cannot be reliably probed with crystallographic techniques owing to its embedded nanocrystalline configuration. Here we show a high-pressure approach which exploits the distinctive behaviors under pressure of wurtzite Mg$_x$Zn$_{1-x}$O thin films with different Mg contents to unveil phase segregation for $x>0.3$. By using ambient conditions photoluminescence (PL), and with optical absorption and PL under high pressure for $x=0.3$ we show that the appearance of a segregated wurtzite phase with a magnesium content of x $\sim$ 0.1 is inherent to the wurtzit…
Photo-electrical and transport properties of hydrothermal ZnO
2016
We performed the studies of optical, photoelectric, and transport properties of a hydrothermal bulk n-type ZnO crystal by using the contactless optical techniques: photoluminescence, light-induced transient grating, and differential reflectivity. Optical studies revealed bound exciton and defect-related transitions between the donor states (at ∼60 meV and ∼240 meV below the conduction band) and the deep acceptor states (at 0.52 eV above the valence band). The acceptor state was ascribed to VZn, and its thermal activation energy of 0.43 eV was determined. A low value of carrier diffusion coefficient (∼0.1 cm2/s) at low excitations and temperatures up to 800 K was attributed to impact the rec…
Partial discharges at different voltage waveshapes: Comparison between two different acquisition systems
2018
In modern HV apparatuses the wide use of electronic converters, increase the stress on the involved insulation systems and thus affect the reliability of the whole power grid. Additionally, such non-sinusoidal voltage shapes contain high gradient flanks that create problems in the detection of partial discharge (PD) activity. The aim of this paper is to discuss the methodology on how to suitably approach PD detection in insulation systems exposed to various voltage waveshapes in general by comparing two different measuring systems. The first one, equipped with a resonant PD decoupler, designed specifically for detection at typical power electronic waveshapes and the other one, based on an a…
SIC based solid state protections switches for space applications
2017
Development and technology maturation of Silicon Carbide (SiC) power transistors over the last 15 years has motivated its study in aerospace systems. When compared with Si devices, superior voltage blocking capacity and the capability of operation at higher temperatures, give important advantages in space power electronics applications, similar to what happens in terrestrial electronics. This paper discusses the use of SiC power transistors for Solid State Power Switches especially addressed to the space segment. Two applications will be covered, the first is the Solid State Shunt Switch, widely used in high power Direct Energy Transfer (DET) photovoltaic power regulators and the second is …
High-pressure study of the infrared active modes in wurtzite and rocksalt ZnO
2011
International audience; We present a high-pressure study of ZnO carried out in the mid- to far-infrared frequency domain with the aim of characterizing the optic modes of wurtzite and rocksalt ZnO. We obtained the pressure coefficients of the E1(TO), E1(LO), A1(TO), and A1(LO) modes of the low-pressure wurtzite phase and compare them with previous Raman measurements. The optical modes of the high-pressure rocksalt phase are infrared active, so we were able to determine their wave numbers and pressure dependencies. In the wurtzite phase, high pressure induces a slight decrease in both longitudinal and transverse effective charges. The decrease is more pronounced in the rocksalt phase.
Half-Heusler compounds: novel materials for energy and spintronic applications
2012
Half-Heusler compounds are an impressive class of materials with a huge potential for different applications such as future energy applications and for spintronics. The semiconducting Heusler compounds can be identified by the number of valence electrons. The band gap can be tuned between 0 and 4 eV by the electronegativity difference of the constituents. Magnetism can be introduced in these compounds by using rare-earth elements, manganese or ‘electron’ doping. Thus, there is a great interest in the fields of thermoelectrics, solar cells and diluted magnetic semiconductors. The combination of different properties such as superconductivity and topological edge states leads to new multifunct…
SiC Power Switches Evaluation for Space Applications Requirements
2016
We have evaluated several SiC power switches available on the market, by defining and performing a global test campaign oriented to Space applications requirements, in order to define their main benefits but also the limits of current SiC technology. This allowed to identify a number of target applications where SiC could be used as a technology push for a new generation of space electronics units. Silicon devices qualified for space systems above 600V for the switches and 1200V for the rectifiers are not available due to performances limitations of Si. Among the typical static and dynamic characterization, we have performed temperature and power stress and HTRB tests. More remarkably, we h…