Europium nitride: A novel diluted magnetic semiconductor

Europium nitride is semiconducting and contains non-magnetic \3+, but sub-stoichiometric EuN has Eu in a mix of 2+ and 3+ charge states. We show that at \2+ ~concentrations near 15-20% EuN is ferromagnetic with a Curie temperature as high as 120 K. The \3+ ~polarization follows that of the \2+, confirming that the ferromagnetism is intrinsic to the EuN which is thus a novel diluted magnetic semiconductor. Transport measurements shed light on the likely exchange mechanisms.Comment: 5 page

Tiling the plane without supersymmetry

We present a way of tiling the plane with a regular hexagonal network of defects. The network is stable and follows in consequence of the three-junctions that appear in a model of two real scalar fields that presents $Z_3$ symmetry. The $Z_3$ symmetry is effective in both the vacuum and defect sectors, and no supersymmetry is required to build the network.Comment: Revtex, 4 pages, 1 ps figure; version to appear in Phys. Rev. Let

An examination of the effects of self-regulatory focus on the perception of the media richness: the case of email

Communication is a key element in organizations’ business success. The media richness theory and the channel expansion theory are two of the most influential theories regarding the selection and use of communication media in organizations; however, literature has focused little on the effects of self-regulation by managers and employees in these theories. To analyze these topics, this study develops an empirical investigation by gathering data from 600 managers and employees using a questionnaire. The results suggest that the perception of media richness is positively affected when the individual shows a promotion focus or strategy.Peer ReviewedPostprint (author’s final draft

Surface states and Rashba-type spin polarization in antiferromagnetic MnBi2_2Te4_4

The layered van der Waals antiferromagnet MnBi$_2$Te$_4$ has been predicted to combine the band ordering of archetypical topological insulators such as Bi$_2$Te$_3$ with the magnetism of Mn, making this material a viable candidate for the realization of various magnetic topological states. We have systematically investigated the surface electronic structure of MnBi$_2$Te$_4$(0001) single crystals by use of spin- and angle-resolved photoelectron spectroscopy experiments. In line with theoretical predictions, the results reveal a surface state in the bulk band gap and they provide evidence for the influence of exchange interaction and spin-orbit coupling on the surface electronic structure.Comment: Revised versio

Vortex dynamics in layered superconductors with correlated defects: influence of interlayer coupling

We report a detailed study of the vortex dynamics and vortex phase diagrams of two amorphous Ta_0.3Ge_0.7/Ge multilayered films with intrinsic coplanar defects, but different interlayer coupling. A pinned Bose-glass phase in the more weakly coupled sample exists only below a cross-over field H* in striking contrast to the strongly coupled film. Above H* the flux lines are thought to break up into pancake vortices and the cross-over field is significantly increased when the field is aligned along the extended defects. The two films show different vortex creep excitations in the Bose-glass phase.Comment: zip file: 1 RevTex, 5 figures (png

The unusual electronic structure of the "pseudo-ladder" compound CaCu2O3

Experimental and theoretical studies of the unoccupied electronic structure of CaCu2O3 single crystals have been performed using polarization-dependent x-ray absorption spectroscopy and band structure calculations. The measured hole distribution shows an unusual large number of holes in orbitals parallel to the interlayer direction which is in agreement with the theoretical analysis. CaCu2O3 deviates significantly from the standard pd-sigma cuprate picture. The corresponding strong interlayer exchange is responsible for the missing spin gap generic for other two-leg ladder cuprates.Comment: 4 pages, 3 figures include

Bags, junctions, and networks of BPS and non-BPS defects

We investigate several models of coupled scalar fields that present discrete Z_2, Z_2 x Z_2, Z_3 and other symmetries. These models support topological domain wall solutions of the BPS and non-BPS type. The BPS solutions are stable, but the stability of the non-BPS solutions may depend on the parameters that specify the models. The BPS and non-BPS states give rise to bags, and also to three-junctions that may allow the presence of networks of topological defects. In particular, we show that the non-BPS defects of a specific model that engenders the Z_3 symmetry give rise to a stable regular hexagonal network of domain walls.Comment: Revtex, 16 pages, 6 ps figures; Shorter version to be published in Phys. Rev.

Single phase nanocrystalline GaMnN thin films with high Mn content

Ga₁ˍₓ Mnₓ Nthin films with a Mn content as high as x=0.18 have been grown using ion-assisted deposition and a combination of Rutherford backscattering spectroscopy and nuclear reaction analysis was used to determine their composition. The structure of the films was determined from x-ray diffraction,transmission electron microscopy, and extended x-ray absorption fine structure(EXAFS). The films are comprised of nanocrystals of random stacked GaMnN and there is no evidence of Mn-rich secondary phases or clusters. EXAFS measurements at the Mn and Ga edge are almost identical to those at the Ga edge from Mn-free nanocrystallineGaNfilms, showing that the Mn occupies the Ga lattice sites, and simulated radial distribution functions of possible Mn-rich impurity phases bear no resemblance to the experimental data. The results indicate that these are the most heavily Mn-doped single phase GaNfilms studied to date.The authors gratefully acknowledge financial support from the New Zealand Foundation for Research Science and Technology through its New Economy Research Fund, and through a postdoctoral fellowship of one of the authors B.J.R.. The work of the MacDiarmid Institute is supported by a New Zealand Centre of Research Excellence award. Another author S.G. wishes to thank Education New Zealand for financial support of the EXAFS measurements

Novel multiple sclerosis susceptibility loci implicated in epigenetic regulation

We conducted a genome-wide association study (GWAS) on multiple sclerosis (MS) susceptibility in German cohorts with 4888 cases and 10,395 controls. In addition to associations within the major histocompatibility complex (MHC) region, 15 non-MHC loci reached genome-wide significance. Four of these loci are novel MS susceptibility loci. They map to the genes L3MBTL3, MAZ, ERG, and SHMT1. The lead variant at SHMT1 was replicated in an independent Sardinian cohort. Products of the genes L3MBTL3, MAZ, and ERG play important roles in immune cell regulation. SHMT1 encodes a serine hydroxymethyltransferase catalyzing the transfer of a carbon unit to the folate cycle. This reaction is required for regulation of methylation homeostasis, which is important for establishment and maintenance of epigenetic signatures. Our GWAS approach in a defined population with limited genetic substructure detected associations not found in larger, more heterogeneous cohorts, thus providing new clues regarding MS pathogenesis