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This Week at Physics

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Events on Friday, March 23rd, 2012

Theory Seminar (High Energy/Cosmology)
Confronting Top AFB with Parity Violation Constraints
Time: 2:00 pm
Place: 5280 Chamberlin Hall
Speaker: Ian-Woo Kim, University of Michigan
Abstract: We consider the implications of low-energy precision tests of parity violation on t-channel mediator models explaining the top AFB excess measured by CDF and D0. Flavor-violating u-t or d-t couplings of new scalar or vector mediators generate at one-loop an anomalous contribution to the nuclear weak charge. As a result, atomic parity violation constraints disfavor at >3 sigma t-channel models that give rise to a greater than 20% AFB at the parton level for M_tt > 450 GeV while not producing too large a top cross-section. Even stronger constraints are expected through future measurements of the proton weak charge by the Q-Weak experiment.
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Physics Department Colloquium
The quantum and classical properties of spins on surfaces
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Andreas Heinrich, IBM Almaden Research Lab
Abstract: The scanning tunneling microscope has been an extremely successful experimental tool because of its atomic-scale spatial resolution. In recent years this has been combined with the use of low temperatures, culminating in precise atom manipulation and spectroscopy with microvolt energy resolution. A cluster of magnetic atoms on a surface behaves similar to a classical magnetic particle: itaEuroTMs magnetization points along an easy-axis direction in space and magnetization reversal requires sufficient thermal energy to overcome a barrier. In this talk we will discuss how many atoms it takes to create such creates, which offers crucial insights into the size limits of stable magnetic nanoparticles. When the number of atoms becomes too small we observe quantum tunneling of magnetization aEuro&quot; in the present case of the aEurooeclassicalaEuro Neel vector. Single atoms that are slightly decoupled from conducting substrates behave more like quantum mechanical entities. These can be studied with inelastic tunneling spectroscopy, a technique we coined spin-excitation spectroscopy. With this approach it is possible to measure the energy eigenstates of the quantum spin Hamiltonian that describes spins on surfaces with high precision. We will introduce its application to the measurement of the Zeeman energy, to magneto-crystalline anisotropy, and to spin-spin coupling via a superexchange interaction.

Dr. Andreas Heinrich Bio
Andreas Heinrich leads a research team at IBM's Almaden Research Center focused on exploring atomic-scale structures for possible applications in computation and datastorage. In January 2012 Heinrich and his team presented the worldaEuroTMs smallest magnetic data storage elements consisting of only 12 magnetic atoms. The work was published in the highest ranking scientific journal, Science, and widely reported in the media, including the New York Times. This work was based on a long-term research effort in HeinrichaEuroTMs team that started with the exploration of the magnetic properties of individual magnetic atoms on surfaces over ten years ago, highlighting IBMaEuroTMs commitment to long-term, exploratory research. Heinrich regularly gives invited lectures and seminars, including plenary lectures at leading international conferences. His main interest is in the exploration of the exciting world of atoms and structures built with atomic-scale precision and in educating the public on the amazing world of nanoscience. Heinrich is both a scientist and an engineer with a keen interest in advancing the experimental capabilities of state-of-the-art research tools. He and his team recently improved the time resolution of scanning tunneling microscopes aEuro" the mot advanced tool for atomic-scale studies on surfaces aEuro" by a factor of 1 million, another breakthrough paper published in Science in 2010. HeinrichaEuroTMs longer-term interest lies in the emerging field of quantum computation, where he hopes to demonstrate the use of single magnetic atoms on surfaces as qubits. Quantum computation has the potential to vastly improve computational performances of computers by taking advantage of the intriguing world of quantum mechanics that governs the properties of atoms. A native of Germany, Heinrich received his PhD in 1998 from the University of Goettingen in Germany and joined IBM in the same year as a postdoc in Dr. Donald EigleraEuroTMs team. Eigler is world-renowned for being the first person to reproducibly move individual atoms on surfaces, a tradition carried on proudly in HeinrichaEuroTMs research efforts.
Host: Himpsel
Poster: http://www.physics.wisc.edu/twap/posters/2012/2308.pdf
Video: http://www.physics.wisc.edu/vod/2012/03/23.html
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