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This Week at Physics

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Events on Thursday, April 14th, 2011

R. G. Herb Condensed Matter Seminar
Interface engineering in epitaxial oxide heterostructures
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Alex Demkov, University of Texas at Austin
Abstract: The astounding progress of recent years in the area of oxide deposition has made possible the creation of oxide heterostructures with atomically abrupt interfaces. The ability to control the length scale, strain, and orbital order in these materials structures offers a uniquely rich toolbox for condensed matter physicists. Because the oxide layers are very thin, the physics is often controlled by the interface. The electronic properties of oxide interfaces are governed by a subtle interplay of many competing mechanisms such as polar catastrophe, Jahn-Teller coupling, electron correlation, defects, and phase stability. It is not clear which, if any, of these systems will find applications in future high-tech devices. However, they undoubtedly hold tremendous promise, particularly when integrated with conventional semiconductors such as Si.

In this talk I will review our recent results in theoretical modeling and experimental realization of several epitaxial oxide heterostructures. I will set the stage with a brief discussion of the n-type conductive SrTiO3/LaA1O3 interface [1]. The origin of charge in this nominally insulating system is still under intense debate, and the difficulties are, in my opinion, generic to the entire field. Our theoretical results are consistent with the originally proposed polar catastrophe model, should the field be indeed stabilized in polar LaA1O3. However, our results indicate that this may be difficult to achieve. I then will discuss extrinsic magnetoelectric coupling at the interface of a perovskite ferroelectric and conventional ferromagnet [2,3]. In contrast with the previously proposed models, the structure we consider offers the robust, linear coupling. If time permits, I will describe our efforts to achieve the monolithic integration of ferromagnetic oxide LaCoO3(LCO) and silicon for possible applications in spintronics [4]. The integration is achieved via the single crystal SrTiO3 (STO) buffer epitaxially grown on Si. The intermediate spin state is stabilized by epitaxial strain at the STO/LCO interface.

1. J. K. Lee and A. A. Demkov, Phys. Rev. B 78, 193104 (2008).
2. T. Cai, Q. Niu, J. K. Lee, Na Sai, and A. A. Demkov, Phys. Rev. B 80, 140415(R) (2009).
3. J. K. Lee, Na Sai, T. Cai, Q. Niu and A. A. Demkov, Phys. Rev. B 81, 144425 (2010).
4. A. Posadas, M. Berg, H. Seo, D. J. Smith, H. Celio, A. P. Kirk, D. Zhernokletov, R. M. Wallace, A. de Lozanne, and A. A. Demkov, Appl. Phys. Lett. 98, 055104 (2011).
Host: Susan Coppersmith & Irena Knezevic
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Astronomy Colloquium
The new world of Gamma Ray Astronomy
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Lucy Fortson, University of Minnesota
Abstract: With the third generation ground-based gamma-ray telescopes delivering over a hundred new TeV emitting objects and with the new Fermi satellite providing greatly improved sensitivity in the GeV energy regime, gamma ray astronomy is entering a golden age. I will first review the basics of ground-based gamma-ray astronomy and the Air Cherenkov Telescope method of detection. I will then describe VERITAS - an array of four gamma ray telescopes located at Mt. Hopkins, Arizona - and some of the recent results from the first few years of the VERITAS observing program, paying attention to the observations of several new TeV emitting active galactic nuclei. I will close with a look at the future of ground-based gamma ray astronomy with the CTA - the proposed array of 36-100 Cherenkov Telescopes.
Host: Prof Andrew Sheinis
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