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This Week at Physics

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Events During the Week of September 22nd through September 29th, 2019

Monday, September 23rd, 2019

No events scheduled

Tuesday, September 24th, 2019

Chaos & Complex Systems Seminar
How solar energy became cheap: A model for low-carbon innovation
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Greg Nemet, La Follett School of Public Affairs
Abstract: La Follette School Professor Greg Nemet will discuss how solar energy became inexpensive and how that path can serve as a model for other low-carbon technologies. However, other technologies would have to progress much faster than solar energy to be helpful for climate change.
Host: Clint Sprott
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Wednesday, September 25th, 2019

Theory Seminar (High Energy/Cosmology)
An Entropic Bound on the Lifetime of De Sitter Space
Time: 4:00 pm
Place: 5280 Chamberlin Hall
Speaker: Lars Aalsma, UW-Madison dept of Physics
Abstract: Abstract: What does the finiteness of the de Sitter entropy teach us about cosmology? In this talk, I will present evidence that it puts a bound on the amount of (quasi-)exponential expansion that can be sustained in semi-classical gravity. We will see how this bound arises by considering a new quantum state of de Sitter space - the Unruh-de Sitter state - which is the cosmological analogue of the Unruh state that describes evaporating black holes. I will compare and contrast the obtained bound with other recent works that suggest that quantum (gravity) effects limit the lifetime of de Sitter space.
Host: Nicholas Orlofsky
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Thursday, September 26th, 2019

R. G. Herb Condensed Matter Seminar
Spin transport in ferromagnet-InSb nanowire quantum devices
Time: 11:00 am
Place: 5310 Chamberlin Hall
Speaker: Vlad Pribiag, University of Minnesota
Abstract: Topological excitations such as Majorana fermions provide unique pathways to fault-tolerant quantum computing. Recent progress in this direction has been enabled by proximity effects between non-superconducting materials and superconductors; however, further breakthroughs leading to topological quantum computation require developing new material systems that integrate semiconductors not only with superconductors, but also with epitaxial ferromagnets or antiferromagnets. Currently, Majorana devices based on semiconductors require application of an external magnetic field to induce spin splitting and open a helical gap – necessary to realize an odd-parity topological superconductor. However, the presence of this magnetic field limits the robustness of topological properties (by weakening the induced superconductivity). Moreover, the stringent requirements on its orientation with respect to the device greatly restrict the scalability of Majorana-based quantum information systems. A promising path forward is to realize Majorana modes without an applied magnetic field by closely integrating ferromagnets or antiferromagnets with semiconductors and superconductors. With this motivation, we have been studying ballistic InSb nanowire devices with ferromagnetic contacts [1]. I will discuss the results of magneto-transport measurements on these devices spanning from the many-modes regime to few modes, and will show that the magnetoresistance displays hysteretic features across this entire range of conductance regimes. I will discuss possible physical mechanisms underlying these observations, as well as implications for the development of Majorana devices that could operate without the need for external magnetic fields.
Host: Alex Levchenko
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Cosmology Journal Club
Time: 12:00 pm
Place: 5242 Chamberlin Hall
Abstract: Please visit the following link for more details:
http://cmb.physics.wisc.edu/journal/index.html
Feel free to bring your lunch!
If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Ross Cawthon (cawthon@wisc.edu) and Santanu Das (sdas33@wisc.edu).
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WISELI Seminar
Physics In Concert With The Arts
Time: 4:00 pm
Place: 4274 Chamberlin Hall
Speaker: Agnes Mocsy, Pratt Institute
Abstract: This talk's journey will depart from the often present science-art dichotomy, exploring the complicated, often unexpected relationship that physics and the arts share. This complex relationship provides opportunities for fresh storytelling, in particular physics narratives embedded in a wider culture and interdisciplinary explorations in classrooms and beyond. I argue that science and the arts acting in concert may deliver benefits beyond science communication, addressing questions of social justice, and become an influencer of a more equitable world.
Host: Women and Gender Minorities in Physics (GMaWiP)
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Friday, September 27th, 2019

Physics Department Colloquium
Superconductivity in Nickelates: Similarities and Differences from Cuprates
Time: 3:30 pm
Place: 2241 Chamberlin Hall
Speaker: Michael Norman, Argonne National Lab
Abstract: The recent discovery of superconductivity in Sr-doped NdNiO2 has refocused attention on the relation of nickelates to cuprates. First I review the experimental situation, including earlier work on trilayer nickelates, as well as the new work on infinite-layer nickelates. Next I comment on various proposed models, including charge-transfer, Mott, and Kondo. Then I relate these models to the electronic structure of nickelates, contrasting this with cuprates. Finally, I comment on relevant parameters in regards to the observation of superconductivity.
Host: Alex Levchenko
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