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Browsing by Author "Kallaher, R. L."

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    Measurement by antilocalization of interactions between InAs surface electrons and magnetic surface species
    Zhang, Y.; Kallaher, R. L.; Soghomonian, Victoria G.; Heremans, Jean J. (American Physical Society, 2013-02-25)
    We show that antilocalization measurements can be used to experimentally study the interactions between InAs surface electrons and local moments of the rare earth ions Sm3+, Gd3+, and Ho3+ on the surface. Magnetic spin-flip scattering and spin-orbit scattering of the accumulation layer electrons are affected by the proximity of the rare earth ions. The spin-flip rate carries information about magnetic interactions. Within the temperature range studied, Sm3+ and Gd3+ yield temperature-independent electron spin-flip rates in proportion to their magnetic moments. In proximity to Ho3+ the InAs electrons however show a spin-flip rate increasing with temperature. We interpret the spin-flip rate due to Ho3+ as resulting from transitions between closely spaced energy levels of the ion on the surface. The experiments also show that the strength of spin-orbit interaction can be modified by the surface species. DOI: 10.1103/PhysRevB.87.054430
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    Spin and phase coherence lengths in InAs wires with diffusive boundary scattering
    Kallaher, R. L.; Heremans, Jean J.; Van Roy, W.; Borghs, G. (American Physical Society, 2013-11-07)
    Measurements of low-temperature magnetotransport in lithographic wires of submicron widths fabricated from high-mobility AlGaSb/InAs/AlGaSb two-dimensional electron system heterostructures are presented. The dependence of the spin and phase coherence lengths on wire width and diffusion constant is investigated by analyzing the conductance in low applied magnetic fields with antilocalization models. Predominantly diffusive boundary scattering is deduced from the magnitude and wire width dependence of the conductance. Diffusive boundary scattering leads to a diffusion constant decreasing with wire width and hence allows the dependence of spin coherence on wire width and diffusion constant to be investigated concurrently. The spin coherence lengths are experimentally found to be proportional to the ratio of the diffusion constant to wire width. The phase coherence lengths follow Nyquist decoherence for low-dimensional wires.
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    Spin and phase coherence lengths in n-InSb quasi-one-dimensional wires
    Kallaher, R. L.; Heremans, Jean J.; Goel, N.; Chung, S. J.; Santos, M. B. (American Physical Society, 2010-01-15)
    We present measurements of the magnetoconductance of quasi-one-dimensional wires fabricated on a two-dimensional electron system in an InSb/InAlSb heterostructure. The width and temperature dependence of the spin and phase coherence lengths in the narrow wires are examined by analyzing the magnetoconductance in antilocalization theory, modified to account for ballistic transport. The experiments indicate that the confined geometry can enhance spin coherence lengths in systems not in the motional narrowing regime and in the presence of strong cubic Dresselhaus spin-orbit interaction. Experimentally, the spin coherence lengths are found to be inversely proportional to wire width and to display a weak temperature dependence. For all wire widths the phase coherence length, after correction for finite length effects, shows a temperature dependence indicative of phase decoherence via the one-dimensional Nyquist mechanism.
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    Spin and phase coherence measured by antilocalization in n-InSb thin films
    Kallaher, R. L.; Heremans, Jean J. (American Physical Society, 2009-02-25)
    The spin and phase coherence times of the itinerant electrons in n-InSb thin films were experimentally determined by analyzing the low-temperature magnetoresistance in antilocalization theory. The results indicate a very weak temperature dependence below 10 K for the spin coherence time. The dependence of the spin coherence time on carrier density demonstrates that the Elliott-Yafet mechanism is predominantly responsible for electron-spin relaxation in n-type InSb at low temperatures. The phase coherence time follows an inverse temperature dependence, in accordance with the electron-electron Nyquist dephasing mechanism.
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    Spin-orbit interaction determined by antilocalization in an InSb quantum well
    Kallaher, R. L.; Heremans, Jean J.; Goel, N.; Chung, S. J.; Santos, M. B. (American Physical Society, 2010-02-02)
    The magnetoresistance at temperatures below 20 K in an n-InSb/In(0.85)Al(0.15)Sb two-dimensional electron system is studied and described in terms of antilocalization due to quantum interference under strong spin-orbit interaction. The spin-orbit interaction coefficients are extracted by fitting the magnetoresistance data to an antilocalization theory distinguishing the Rashba and Dresselhaus contributions. A good agreement between magnetoresistance data and theory suggests a Rashba coefficient vertical bar alpha vertical bar approximate to 0.03 eV angstrom and a Dresselhaus coefficient gamma approximate to 490 eV angstrom(3). A strong contribution from the Dresselhaus term leads to pronounced anisotropy in the energy splitting induced by spin-orbit interaction in the two-dimensional electron dispersion.