Intrinsic defects in silicon carbide LED as a perspective room temperature single photon source in near infrared

Generation of single photons has been demonstrated in several systems. However, none of them satisfies all the conditions, e.g. room temperature functionality, telecom wavelength operation, high efficiency, as required for practical applications. Here, we report the fabrication of light emitting diodes (LEDs) based on intrinsic defects in silicon carbide (SiC). To fabricate our devices we used a standard semiconductor manufacturing technology in combination with high-energy electron irradiation. The room temperature electroluminescence (EL) of our LEDs reveals two strong emission bands in visible and near infrared (NIR), associated with two different intrinsic defects. As these defects can potentially be generated at a low or even single defect level, our approach can be used to realize electrically driven single photon source for quantum telecommunication and information processing

Pseudobinary Fe4Ti3S8 compound with a NiAs-type structure: Effect of Ti for Fe substitution

The transition metal sulfide Fe4Ti3S8 with 7:8 composition has been synthesized and studied by using X-ray diffraction, magnetization and electrical resistivity measurements. This compound exhibits a monoclinic crystal lattice (space group I12/m1). The substitution of Ti for Fe in Fe7S8 is found to result in a lowering of the Curie temperature (TC ≈ 205 K), in a larger value of the coercive field (Hc ∼ 9 kOe at low temperatures) and in a substantial growth of the resultant magnetic moment per formula unit (μFU) in comparison with Fe7S8. An enhanced value of μFU is attributed to the preferential substitution of Ti in alternating cation layers. From the paramagnetic susceptibility measured within temperature interval (250-350) K, a reduced value of the effective moment per iron (μFe ∼ 2.4μB) was determined. The electrical resistivity of Fe4Ti3S8 shows a non-metallic behavior and is affected by magnetic ordering. © 2013 Elsevier Masson SAS. All rights reserved

Sympathetic cooling in a mixture of diamagnetic and paramagnetic atoms

We have experimentally realized a hybrid trap for ultracold paramagnetic rubidium and diamagnetic ytterbium atoms by combining a bichromatic optical dipole trap for ytterbium with a Ioffe-Pritchard-type magnetic trap for rubidium. In this hybrid trap, sympathetic cooling of five different ytterbium isotopes through elastic collisions with rubidium was achieved. A strong dependence of the interspecies collisional cross section on the mass of the ytterbium isotope was observed.Comment: 4 pages, 4 figure

The CCFM Monte Carlo generator CASCADE 2.2.0

CASCADE is a full hadron level Monte Carlo event generator for ep, \gamma p and p\bar{p} and pp processes, which uses the CCFM evolution equation for the initial state cascade in a backward evolution approach supplemented with off - shell matrix elements for the hard scattering. A detailed program description is given, with emphasis on parameters the user wants to change and variables which completely specify the generated events

Pyrrolysine and Selenocysteine Use Dissimilar Decoding Strategies

Selenocysteine (Sec) and pyrrolysine (Pyl) are known as the 21st and 22nd amino acids in protein. Both are encoded by codons that normally function as stop signals. Sec specification by UGA codons requires the presence of a cis-acting selenocysteine insertion sequence (SECIS) element. Similarly, it is thought that Pyl is inserted by UAG codons with the help of a putative pyrrolysine insertion sequence (PYLIS) element. Herein, we analyzed the occurrence of Pyl-utilizing organisms, Pyl-associated genes, and Pyl-containing proteins. The Pyl trait is restricted to several microbes, and only one organism has both Pyl and Sec. We found that methanogenic archaea that utilize Pyl have few genes that contain in-frame UAG codons, and many of these are followed with nearby UAA or UGA codons. In addition, unambiguous UAG stop signals could not be identified. This bias was not observed in Sec-utilizing organisms and non-Pyl-utilizing archaea, as well as with other stop codons. These observations as well as analyses of the coding potential of UAG codons, overlapping genes, and release factor sequences suggest that UAG is not a typical stop signal in Pyl-utilizing archaea. On the other hand, searches for conserved Pyl-containing proteins revealed only four protein families, including methylamine methyltransferases and transposases. Only methylamine methyltransferases matched the Pyl trait and had conserved Pyl, suggesting that this amino acid is used primarily by these enzymes. These findings are best explained by a model wherein UAG codons may have ambiguous meaning and Pyl insertion can effectively compete with translation termination for UAG codons obviating the need for a specific PYLIS structure. Thus, Sec and Pyl follow dissimilar decoding and evolutionary strategies

Room-temperature near-infrared silicon carbide nanocrystalline emitters based on optically aligned spin defects

Bulk silicon carbide (SiC) is a very promising material system for bio-applications and quantum sensing. However, its optical activity lies beyond the near infrared spectral window for in-vivo imaging and fiber communications due to a large forbidden energy gap. Here, we report the fabrication of SiC nanocrystals and isolation of different nanocrystal fractions ranged from 600 nm down to 60 nm in size. The structural analysis reveals further fragmentation of the smallest nanocrystals into ca. 10-nm-size clusters of high crystalline quality, separated by amorphization areas. We use neutron irradiation to create silicon vacancies, demonstrating near infrared photoluminescence. Finally, we detect, for the first time, room-temperature spin resonances of these silicon vacancies hosted in SiC nanocrystals. This opens intriguing perspectives to use them not only as in-vivo luminescent markers, but also as magnetic field and temperature sensors, allowing for monitoring various physical, chemical and biological processes.Comment: 5 pages, 4 figure

Theory of high-energy emission from the pulsar/Be-star system PSR 1259−-63 I: radiation mechanisms and interaction geometry

We study the physical processes of the PSR B1259-63 system containing a 47 ms pulsar orbiting around a Be star in a highly eccentric orbit. Motivated by the results of a multiwavelength campaign during the January 1994 periastron passage of PSR B1259-63, we discuss several issues regarding the mechanism of high-energy emission. Unpulsed power law emission from the this system was detected near periastron in the energy range 1-200 keV. We find that the observed high energy emission from the PSR B1259-63 system is not compatible with accretion or propeller-powered emission. Shock-powered high-energy emission produced by the pulsar/outflow interaction is consistent with all high energy observations. By studying the evolution of the pulsar cavity we constrain the magnitude and geometry of the mass outflow outflow of the Be star. The pulsar/outflow interaction is most likely mediated by a collisionless shock at the internal boundary of the pulsar cavity. The system shows all the characteristics of a {\it binary plerion} being {\it diffuse} and {\it compact} near apastron and periastron, respectively. The PSR B1259-63 cavity is subject to different radiative regimes depending on whether synchrotron or inverse Compton (IC) cooling dominates the radiation of electron/positron pairs advected away from the inner boundary of the pulsar cavity. The highly non-thermal nature of the observed X-ray/gamma-ray emission near periastron establishes the existence of an efficient particle acceleration mechanism within a timescale shown to be less than $\sim 10^2-10^3$ s. A synchrotron/IC model of emission of e\pm-pairs accelerated at the inner shock front of the pulsar cavity and adiabatically expanding in the MHD flow provides an excellent explanation of the observed time variableX-ray flux and spectrum from the PSRComment: 68 pages, accepted for publication in the Astrophys. J. on Aug. 26, 199

Critical behavior study of magnetic transitions in Dy3Co single crystals

An ac photopyroelectric calorimeter has been used to study the critical behaviour of the magnetic transitions in Dy3Co measuring thermal diffusivity, specific heat and thermal conductivity, at low temperature. There are two phase transitions, both of which present singularities in the three variables. The antiferromagnetic to paramagnetic phase transition at 42 K complies with the short range, isotropic universality class, 3D-Heisenberg (alfaexp = -0.133 for specific heat, bexp = -0.145 for thermal diffusivity, alfatheor = btheor = -0.13). In the case of the lower transition where there is a rearrangement of the antiferromagnetic spin ordering at 32 K the critical behavior shows a deviation from isotropy. These results are linked to magnetic measurements already found in literature.This work has been supported by Universidad del País Vasco/Euskal Herriko Unibertsitatea (UPV/EHU-GIU16/93) and also partially supported by FASO of Russia (themes No 01201463328 and 01201463334)