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This Week at Physics

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Events on Tuesday, February 26th, 2013

R. G. Herb Condensed Matter Seminar
Gate control of single electron spin in III-V semiconductor quantum dots: Anisotropy effects
Time: 10:00 am
Place: 5280 Chamberlin Hall
Speaker: Sanjay Prabhakar, Wilfrid Laurier University
Abstract: Among recent proposals for next-generation non-charge-based logic is the notion that a single electron can be trapped and its spin can be manipulated through the application of gate potentials. In the first part of my talk, I present numerical simulations of such spins in single-electron devices for realistic asymmetric confining potentials in two-dimensional electrostatically confined quantum dots. Using both analytical and numerical techniques, I show that breaking the in-plane rotational symmetry of the confining potential leads to a significant effect on the tunability of the g- factor and on the spin-flip rate mediated by phonon with applied gate potentials. In particular, anisotropy either extends the range of the tunability of the g-factor and spin-hot spot to larger quantum dots or viceversa. For example, anisotropy reduces the tunability of the g-factor and spin hot spot to smaller quantum dots radius as well as to smaller magnetic fields if we keep the area of the symmetric and asymmetric quantum dots same. It is well known that the cusp-like structure due to accidental degeneracy in the phonon mediated spin-flip rate can be seen only for the case of pure Rashba spin-orbit coupling in symmetric quantum dots. I present new analytical and numerical results which show that the cusp-like structure can be seen for pure Dresselhaus spin-orbit coupling case in asymmetric quantum dots.

In the second part of my talk, I investigate the geometric phase induced on the spin states during the adiabatic movement of the III-V semiconductor quantum dots in the plane of two-dimensional electron gas under the influence of applied gate potential along the lateral direction. Here, I present the spin-flip probabilities during the adiabatic evolution in the presence of the Rashba and the Dresselhaus linear spin-orbit interactions. I use the Feynman disentanglement technique to determine the non-Abelian Berry phase and find exact analytical expressions for three special cases: (a) the pure Rashba spin-orbit coupling, (b) the pure Dresselhause linear spin-orbit coupling, and (c) the mixture of the Rashba and Dresselhaus spin-orbit couplings with equal strength. For a mixture of the Rashba and the Dresselhaus spin-orbit couplings with unequal strengths, I obtain numerical results by solving the Riccati equation originating from the disentangling procedure. I find that the spin-flip probability in the presence of the mixed spin-orbit couplings is generally larger than those for the pure Rashba case and for the pure Dresselhaus case, and that the complete spin-flip takes place only when the Rashba and the Dresselhaus spin-orbit couplings are mixed symmetrically.

References:

Gate control of a quantum dot single-electron spin in realistic confining potentials: Anisotropy effects; Sanjay Prabhakar and James Raynolds, phys. Rev. B 79, 195307 (2009).

Manipulation of single electron spin in a GaAs quantum dot through the application of geometric phases: The Feynman disentangling technique; Sanjay Prabhakar, James E Raynolds, Akira Inomata and Roderick Melnik, Phys. Rev. B 82, 195306 (2010).

Manipulation of the Lande g-factor in InAs quantum dots through the application of anisotropic gate potentials; Sanjay Prabhakar, James E Raynolds and Roderick Melnik, Phys. Rev. B 84, 155208 (2011).

The influence of anisotropic gate potentials on the phonon induced spin-flip rate in GaAs quantum dots; Sanjay Prabhakar, Roderick Melnik and Luis L Bonilla, Applied Physics Letters 100, 023108 (2012).
Host: Friesen
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Chaos & Complex Systems Seminar
The brave cyberworld of science communication
Time: 12:05 pm
Place: 4274 Chamberlin (Refreshments will be served)
Speaker: Dominique Brossard, UW Department of Life Sciences and Communication
Abstract: As more and more individuals turn to online environments to follow scientific issues and find information about science, recent research is science communication has focused on examining how these online environments may shape public attitudes toward science and public understanding of science. This introduction will discuss patterns of science communication online and present recent research findings in that area. Notably, I will introduce results of an experiment with a national sample of the American population testing the effects of comments on science blogs on readersaEuroTM attitudes toward the scientific issues covered in such blogs. I will also explain the effects of current practices related to online searches on public understanding of science. In light of these results, challenges and opportunities for science as an institution as well as for science and society will be discussed.
Host: Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
Recent Discoveries in Neutrino Physics
Time: 1:20 pm
Place: 2223 Chamberlin
Speaker: Karsten Heeger, University of Wisconsin Department of Physics
Abstract: A series of weekly presentations and discussions of current research topics in physics by the scientists involved in those studies designed to expose students to the topics and excitement of the research frontier.
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