Magnetic Field Induced Spin Polarization of AlAs Two-dimensional Electrons

Two-dimensional (2D) electrons in an in-plane magnetic field become fully spin polarized above a field B_P, which we can determine from the in-plane magnetoresistance. We perform such measurements in modulation-doped AlAs electron systems, and find that the field B_P increases approximately linearly with 2D electron density. These results imply that the product |g*|m*, where g* is the effective g-factor and m* the effective mass, is a constant essentially independent of density. While the deduced |g*|m* is enhanced relative to its band value by a factor of ~ 4, we see no indication of its divergence as 2D density approaches zero. These observations are at odds with results obtained in Si-MOSFETs, but qualitatively confirm spin polarization studies of 2D GaAs carriers.Comment: 4 pages, 5 figure

Schwinger-Keldysh Approach to Disordered and Interacting Electron Systems: Derivation of Finkelstein's Renormalization Group Equations

We develop a dynamical approach based on the Schwinger-Keldysh formalism to derive a field-theoretic description of disordered and interacting electron systems. We calculate within this formalism the perturbative RG equations for interacting electrons expanded around a diffusive Fermi liquid fixed point, as obtained originally by Finkelstein using replicas. The major simplifying feature of this approach, as compared to Finkelstein's is that instead of $N \to 0$ replicas, we only need to consider N=2 species. We compare the dynamical Schwinger-Keldysh approach and the replica methods, and we present a simple and pedagogical RG procedure to obtain Finkelstein's RG equations.Comment: 22 pages, 14 figure

The Parallel Magnetoconductance of Interacting Electrons in a Two Dimensional Disordered System

The transport properties of interacting electrons for which the spin degree of freedom is taken into account are numerically studied for small two dimensional diffusive clusters. On-site electron-electron interactions tend to delocalize the electrons, while long-range interactions enhance localization. On careful examination of the transport properties, we reach the conclusion that it does not show a two dimensional metal insulator transition driven by interactions. A parallel magnetic field leads to enhanced resistivity, which saturates once the electrons become fully spin polarized. The strength of the magnetic field for which the resistivity saturates decreases as electron density goes down. Thus, the numerical calculations capture some of the features seen in recent experimental measurements of parallel magnetoconductance.Comment: 10 pages, 6 figure

2FGL J0846.0+2820 opt. counterpart follow-up

Item does not contain fulltextThe γ-ray source was first detected as 2FGL J0846.0+2820 (Nolan+ 2012, J/ApJS/199/31), listed in the second full catalog of Fermi-LAT sources, based on the first two years of LAT data obtained from 2008 August to 2010 August using the earlier P7V6 instrument response functions (IRFs). See section 2.1. The γ-ray source 2FGL J0846.0+2820 was selected for follow-up study based on a search of positional coincidences of periodic optical variables found in the Catalina Sky Surveys Data Release-1 (CSS -DR1; Drake+ 2014, J/ApJS/213/9) catalog with Fermi-LAT sources. To analyze the CSS photometry of this variable, we retrieved 471 CSS photometric measurements of the variable optical counterpart taken between 2005 April 10 and 2013 September 25. See section 2.2.1. We obtained time series photometry of the optical source in B, V, and R bands with the 16-inch PROMPT-5 telescope at Cerro Tololo International Observatory between 2015 February 4 and 2015 June 7. Each observing night consisted of multiple 60s exposures of the target field, which included the candidate optical counterpart to 2FGLJ0846.0+2820 as well as five nearby comparison stars. Our final sample includes 1643 photometric measurements in B, 1038 in V, and 500 in R, with mean magnitudes B=16.73, V=15.95, and R=15.40. See section 2.2.2. We began spectroscopic monitoring of the source with the Goodman Spectrograph on the Southern Astrophysical Research (SOAR) 4.1m telescope on 2014 December 8, continuing through 2016 December 31. We obtained 19 independent SOAR epochs of velocities. We also obtained some low-resolution spectra with OSMOS on the Hiltner 2.4m telescope at the MDM Observatory at Kitt Peak. These spectra were obtained in two to three exposures of 20 minute each on eight epochs from 2016 October 20 to 2017 January 8. See section 3.1. We obtained a high-resolution spectrum with HIRES on the Keck I telescope on 2016 September 25 (R~36000, wavelength range ~3900-8100Å). See section 3.2. Forthcoming X-ray observations will help confirm the connection between the Fermi γ-ray source 2FGL J0846.0+2820 and the optical binary CSS J084621.9+280839. (2 data files).nul

2FGL J0846.0+2820 opt. counterpart follow-up

The γ-ray source was first detected as 2FGL J0846.0+2820 (Nolan+ 2012, J/ApJS/199/31), listed in the second full catalog of Fermi-LAT sources, based on the first two years of LAT data obtained from 2008 August to 2010 August using the earlier P7V6 instrument response functions (IRFs). See section 2.1. The γ-ray source 2FGL J0846.0+2820 was selected for follow-up study based on a search of positional coincidences of periodic optical variables found in the Catalina Sky Surveys Data Release-1 (CSS -DR1; Drake+ 2014, J/ApJS/213/9) catalog with Fermi-LAT sources. To analyze the CSS photometry of this variable, we retrieved 471 CSS photometric measurements of the variable optical counterpart taken between 2005 April 10 and 2013 September 25. See section 2.2.1. We obtained time series photometry of the optical source in B, V, and R bands with the 16-inch PROMPT-5 telescope at Cerro Tololo International Observatory between 2015 February 4 and 2015 June 7. Each observing night consisted of multiple 60s exposures of the target field, which included the candidate optical counterpart to 2FGLJ0846.0+2820 as well as five nearby comparison stars. Our final sample includes 1643 photometric measurements in B, 1038 in V, and 500 in R, with mean magnitudes B=16.73, V=15.95, and R=15.40. See section 2.2.2. We began spectroscopic monitoring of the source with the Goodman Spectrograph on the Southern Astrophysical Research (SOAR) 4.1m telescope on 2014 December 8, continuing through 2016 December 31. We obtained 19 independent SOAR epochs of velocities. We also obtained some low-resolution spectra with OSMOS on the Hiltner 2.4m telescope at the MDM Observatory at Kitt Peak. These spectra were obtained in two to three exposures of 20 minute each on eight epochs from 2016 October 20 to 2017 January 8. See section 3.1. We obtained a high-resolution spectrum with HIRES on the Keck I telescope on 2016 September 25 (R~36000, wavelength range ~3900-8100Å). See section 3.2. Forthcoming X-ray observations will help confirm the connection between the Fermi γ-ray source 2FGL J0846.0+2820 and the optical binary CSS J084621.9+280839. (2 data files)

Codominant inheritance in immunogenetic (IR-gene) systems.

Immunogenetic (IR-gene) systems consist of animals showing different quantitative antibody responses when immunized with similar doses of a given antigen. Strains of animals giving high and low antibody titres are described as high and low responders, respectively. The degree of dominance in F1 hybrid strains, obtained from a cross between high and low responder parents, can readily be calculated using the dominance index formula, which takes the value of +1 for complete dominance, -1 for complete recessivity and the value of zero for no dominance. In reviewing 1527 F1 animals, obtained from ninety-one immunogenetic systems, the degree of diminance (d) was found to be: +0-0076 +/- 0-1053 (mean +/- s.e.), which is close to a value of zero and this is consistent with codominant inheritance. It is suggested that in immunogenetic systems, both alleles are expressed as codominant genes