2,711 research outputs found

    Origin of transition metal clustering tendencies in GaAs based dilute magnetic semiconductors

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    While isovalent doping of GaAs (e.g. by In) leads to a repulsion between the solute atoms, two Cr, Mn, or Fe atoms in GaAs are found to have lower energy than the well-separated pair, and hence attract each other. The strong bonding interaction between levels with t2 symmetry on the transition metal (TM) atoms results in these atoms exhibiting a strong tendency to cluster. Using first-principles calculations, we show that this attraction is maximal for Cr, Mn and Fe while it is minimal for V. The difference is attributed to the symmetry of the highest occupied levels. While the intention is to find possible choices of spintronic materials that show a reduced tendency to cluster, one finds that the conditions that minimize clustering tendencies also minimize the stabilization of the magnetic state.Comment: To appear in Appl. Phys. Let

    Characterizing the Brazilian Term Structure of Interest Rates

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    This paper studies the Brazilian term structure of interest rates and characterizes how the term premia has changed over time. We employ a Kalman filter approach, which is extended to take into account regime switches and overlapping forecasts errors. Empirical evidence suggests that term premia depends on international global liquidity and domestic factors such as the composition of public debt and inflation volatility. These results provide guidance for the formulation of fiscal and monetary policies.

    Supersymmetric extensions of K field theories

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    We review the recently developed supersymmetric extensions of field theories with non-standard kinetic terms (so-called K field theories) in two an three dimensions. Further, we study the issue of topological defect formation in these supersymmetric theories. Specifically, we find supersymmetric K field theories which support topological kinks in 1+1 dimensions as well as supersymmetric extensions of the baby Skyrme model for arbitrary nonnegative potentials in 2+1 dimensions.Comment: Contribution to the Proceedings of QTS7, Prague, August 201

    Extended Supersymmetry and BPS solutions in baby Skyrme models

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    We continue the investigation of supersymmetric extensions of baby Skyrme models in d=2+1 dimensions. In a first step, we show that the CP(1) form of the baby Skyrme model allows for the same N=1 SUSY extension as its O(3) formulation. Then we construct the N=1 SUSY extension of the gauged baby Skyrme model, i.e., the baby Skyrme model coupled to Maxwell electrodynamics. In a next step, we investigate the issue of N=2 SUSY extensions of baby Skyrme models. We find that all gauged and ungauged submodels of the baby Skyrme model which support BPS soliton solutions allow for an N=2 extension such that the BPS solutions are one-half BPS states (i.e., annihilated by one-half of the SUSY charges). In the course of our investigation, we also derive the general BPS equations for completely general N=2 supersymmetric field theories of (both gauged and ungauged) chiral superfields, and apply them to the gauged nonlinear sigma model as a further, concrete example.Comment: 32 pages, Latex fil

    On the Generalized Word Problem for Finitely Presented Lattices.

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    Ph.D. Thesis. University of Hawaiʻi at Mānoa 2018

    Thermodynamics of the BPS Skyrme model

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    One problem in the application of the Skyrme model to nuclear physics is that it predicts too large a value for the compression modulus of nuclear matter. Here we investigate the thermodynamics of the BPS Skyrme model at zero temperature and calculate its equation of state. Among other results, we find that classically (i.e. without taking into account quantum corrections) the compressibility of BPS skyrmions is, in fact, infinite, corresponding to a zero compression modulus. This suggests that the inclusion of the BPS submodel into the Skyrme model lagrangian may significantly reduce this too large value, providing further evidence for the claim that the BPS Skyrme model may play an important role in the description of nuclei and nuclear matter.Comment: Latex, 26 pages, 1 figure; v2: some typos corrected, version accepted for publication in Phys. Rev.
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