The role of symmetry on interface states in magnetic tunnel junctions

When an electron tunnels from a metal into the barrier in a magnetic tunnel junction it has to cross the interface. Deep in the metal the eigenstates for the electron can be labelled by the point symmetry group of the bulk but around the interface this symmetry is reduced and one has to use linear combinations of the bulk states to form the eigenstates labelled by the irreducible representations of the point symmetry group of the interface. In this way there can be states localized at the interface which control tunneling. The conclusions as to which are the dominant tunneling states are different from that conventionally found.Comment: 14 pages, 5 figures, accepted in PRB, v2: reference 3 complete

Seeking the Real Adam Smith and Milton Friedman

In this paper we will analyze the relationship between free market principles and ethics through an exploration of how too many business managers often approach the ideas of Adam Smith and Milton Friedman. In doing so, we aim to provide a thoughtful foundation for future discussions of how we ought to navigate this intersection. We briefly examine questions such as: What is the relationship between the “best” economy in terms of efficiency and the common good for society? Is pursuing one’s individual economic advantage the same as promoting the general interest? As we analyze and discuss these questions, specifically in the context of Smith and Friedman, we also make some alternative normative assertions, grounded in social welfare, about adopting a broader societal perspective for the purpose of business

Structural and magnetic properties of Fe/ZnSe(001) interfaces

We have performed first principles electronic structure calculations to investigate the structural and magnetic properties of Fe/ZnSe(001) interfaces. Calculations involving full geometry optimizations have been carried out for a broad range of thickness of Fe layers(0.5 monolayer to 10 monolayers) on top of a ZnSe(001) substrate. Both Zn and Se terminated interfaces have been explored. Total energy calculations show that Se segregates at the surface which is in agreement with recent experiments. For both Zn and Se terminations, the interface Fe magnetic moments are higher than the bulk bcc Fe moment. We have also investigated the effect of adding Fe atoms on top of a reconstructed ZnSe surface to explore the role of reconstruction of semiconductor surfaces in determining properties of metal-semiconductor interfaces. Fe breaks the Se dimer bond formed for a Se-rich (2x1) reconstructed surface. Finally, we looked at the reverse growth i.e. growth of Zn and Se atoms on a bcc Fe(001) substrate to investigate the properties of the second interface of a magnetotunnel junction. The results are in good agreement with the theoretical and experimental results, wherever available.Comment: 7 pages, 8 figures, accepted for publication in PR

Markov Chain Methods For Analyzing Complex Transport Networks

We have developed a steady state theory of complex transport networks used to model the flow of commodity, information, viruses, opinions, or traffic. Our approach is based on the use of the Markov chains defined on the graph representations of transport networks allowing for the effective network design, network performance evaluation, embedding, partitioning, and network fault tolerance analysis. Random walks embed graphs into Euclidean space in which distances and angles acquire a clear statistical interpretation. Being defined on the dual graph representations of transport networks random walks describe the equilibrium configurations of not random commodity flows on primary graphs. This theory unifies many network concepts into one framework and can also be elegantly extended to describe networks represented by directed graphs and multiple interacting networks.Comment: 26 pages, 4 figure

A new interferometric study of four exoplanet host stars : {\theta} Cygni, 14 Andromedae, {\upsilon} Andromedae and 42 Draconis

Studying exoplanet host stars is of the utmost importance to establish the link between the presence of exoplanets around various types of stars and to understand the respective evolution of stars and exoplanets. Using the limb-darkened diameter (LDD) obtained from interferometric data, we determine the fundamental parameters of four exoplanet host stars. We are particularly interested in the F4 main-sequence star, {\theta} Cyg, for which Kepler has recently revealed solar-like oscillations that are unexpected for this type of star. Furthermore, recent photometric and spectroscopic measurements with SOPHIE and ELODIE (OHP) show evidence of a quasi-periodic radial velocity of \sim150 days. Models of this periodic change in radial velocity predict either a complex planetary system orbiting the star, or a new and unidentified stellar pulsation mode. We performed interferometric observations of {\theta} Cyg, 14 Andromedae, {\upsilon} Andromedae and 42 Draconis for two years with VEGA/CHARA (Mount Wilson, California) in several three-telescope configurations. We measured accurate limb darkened diameters and derived their radius, mass and temperature using empirical laws. We obtain new accurate fundamental parameters for stars 14 And, {\upsilon} And and 42 Dra. We also obtained limb darkened diameters with a minimum precision of \sim 1.3%, leading to minimum planet masses of Msini=5.33\pm 0.57, 0.62 \pm 0.09 and 3.79\pm0.29 MJup for 14 And b, {\upsilon} And b and 42 Dra b, respectively. The interferometric measurements of {\theta} Cyg show a significant diameter variability that remains unexplained up to now. We propose that the presence of these discrepancies in the interferometric data is caused by either an intrinsic variation of the star or an unknown close companion orbiting around it.Comment: 10 pages + 2 pages appendix, 16 figures, accepted for publication in A&

The Deconfinement Phase Transition in One-Flavour QCD

We present a study of the deconfinement phase transition of one-flavour QCD, using the multiboson algorithm. The mass of the Wilson fermions relevant for this study is moderately large and the non-hermitian multiboson method is a superior simulation algorithm. Finite size scaling is studied on lattices of size $8^3\times 4$, $12^3\times 4$ and $16^3\times 4$. The behaviours of the peak of the Polyakov loop susceptibility, the deconfinement ratio and the distribution of the norm of the Polyakov loop are all characteristic of a first-order phase transition for heavy quarks. As the quark mass decreases, the first-order transition gets weaker and turns into a crossover. To investigate finite size scaling on larger spatial lattices we use an effective action in the same universality class as QCD. This effective action is constructed by replacing the fermionic determinant with the Polyakov loop identified as the most relevant Z(3) symmetry breaking term. Higher-order effects are incorporated in an effective Z(3)-breaking field, $h$, which couples to the Polyakov loop. Finite size scaling determines the value of $h$ where the first order transition ends. Our analysis at the end - point, $h_{ep}$, indicates that the effective model and thus QCD is consistent with the universality class of the three dimensional Ising model. Matching the field strength at the end point, $h_{ep}$, to the $\kappa$ values used in the dynamical quark simulations we estimate the end point, $\kappa_{ep}$, of the first-order phase transition. We find $\kappa_{ep}\sim 0.08$ which corresponds to a quark mass of about 1.4 GeV .Comment: LaTex, 25 pages, 18 figure

Search for CP violation in D0 and D+ decays

A high statistics sample of photoproduced charm particles from the FOCUS (E831) experiment at Fermilab has been used to search for CP violation in the Cabibbo suppressed decay modes D+ to K-K+pi+, D0 to K-K+ and D0 to pi-pi+. We have measured the following CP asymmetry parameters: A_CP(K-K+pi+) = +0.006 +/- 0.011 +/- 0.005, A_CP(K-K+) = -0.001 +/- 0.022 +/- 0.015 and A_CP(pi-pi+) = +0.048 +/- 0.039 +/- 0.025 where the first error is statistical and the second error is systematic. These asymmetries are consistent with zero with smaller errors than previous measurements.Comment: 12 pages, 4 figure

A Study of D0 --> K0(S) K0(S) X Decay Channels

Using data from the FOCUS experiment (FNAL-E831), we report on the decay of $D^0$ mesons into final states containing more than one $K^0_S$. We present evidence for two Cabibbo favored decay modes, $D^0\to K^0_SK^0_S K^- \pi^+$ and $D^0\to K^0_SK^0_S K^+ \pi^-$, and measure their combined branching fraction relative to $D^0\to \bar{K} ^0\pi^+\pi^-$ to be $\frac{\Gamma(D^0\to K^0_SK^0_SK^{\pm}\pi^{\mp})}{\Gamma(D^0\to \bar{K} ^0\pi^+\pi^-)}$ = 0.0106 $\pm$ 0.0019 $\pm$ 0.0010. Further, we report new measurements of $\frac{\Gamma(D^0\to K^0_SK^0_SK^0_S)}{\Gamma(D^0\to \bar{K} ^0\pi^+\pi^-)}$ = 0.0179 $\pm$ 0.0027 $\pm$ 0.0026, $\frac{\Gamma(D^0\to K^0\bar{K} ^0)}{\Gamma(D^0\to \bar{K} ^0\pi^+\pi^-)}$ = 0.0144 $\pm$ 0.0032 $\pm$ 0.0016, and $\frac{\Gamma(D^0\to K^0_SK^0_S\pi^+\pi^-)}{\Gamma(D^0\to \bar{K} ^0\pi^+\pi^-)}$ = 0.0208 $\pm$ 0.0035 $\pm$ 0.0021 where the first error is statistical and the second is systematic.Comment: 11 pages, 3 figures, typos correcte

Observation of ZZ production in ppbar collisions at sqrt(s) = 1.96 TeV

We present an observation for ZZ -> l+l-l'+l'- (l, l' = e or mu) production in ppbar collisions at a center-of-mass energy of sqrt(s) = 1.96 TeV. Using 1.7 fb-1 of data collected by the D0 experiment at the Fermilab Tevatron Collider, we observe three candidate events with an expected background of 0.14 +0.03 -0.02 events. The significance of this observation is 5.3 standard deviations. The combination of D0 results in this channel, as well as in ZZ -> l+l-nunubar, yields a significance of 5.7 standard deviations and a combined cross section of sigma(ZZ) = 1.60 +/- 0.63 (stat.) +0.16 -0.17 (syst.) pb.Comment: 7 pages, 1 figure, 2 tables Modified slightly following review proces