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Events on Thursday, November 16th, 2023

R. G. Herb Condensed Matter Seminar
Strongly interacting excitons and electrons in atomically thin semiconducting heterostructures
Time: 10:00 am - 6:00 pm
Place: 5310 Chamberlin
Speaker: You Zhou, U Maryland
Abstract: Heterostructures of atomically thin semiconductors, such as transition metal dichalcogenides (TMDs), have recently emerged as an exciting platform for exploring strongly interacting many-body systems of electrons and excitons. This talk focuses on our recent research investigating strong interactions among excitons and free carriers within these systems, shedding light on their relevance to Mott-Hubbard physics and applications in nonlinear optics and nanophotonics. First, I will discuss how optical pumping in TMD trilayers can induce giant excitonic optical nonlinearity via exciton-hole interactions. I will then describe how we can combine optical pumping and electrostatic gating to independently control the population of excitons and electrons in a TMD moiré system. This approach allows us to probe the intricate phase diagram of a Hubbard model with hybrid Ferionic and Bosonic excitations, leading to the observation of an excitonic Mott insulator. Lastly, I will discuss how one can combine multiple layers of atomically thin excitonic materials to fabricate optical nano-cavities. The emphasis will be on the realization of light-matter interactions that are both chiral and electrically tunable using such cavities, as well as the exploration of intriguing collective emitter states like super- and sub-radiance.
Host: Ilya Esterlis
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Detecting the highest energy neutrinos...with radar? A new tool in the astroparticle toolbox
Time: 2:30 pm - 3:30 pm
Place: Chamberlin 5280 or
Speaker: Steven Prohira, The University of Kansas
Abstract: Detection of ultrahigh energy (UHE) neutrinos is key to identifying the most energetic objects and processes in the universe. These are the sources of UHE cosmic rays that have been detected at earth with energies exceeding 1 Joule per nucleon (roughly the kinetic energy of a bird in flight). As UHE cosmic messengers, neutrinos are unparalleled for their ability to travel from their sources to the Earth, interacting only weakly with matter, and therefore able to traverse great distances unimpeded. UHE neutrinos can also provide a powerful handle on physics beyond the standard model. However, their flux decreases significantly with increasing energy. This, coupled with their weak interaction, makes them very challenging to detect at energies above those successfully probed by IceCube. In this talk, I will discuss the extensive experimental work that has been performed to meet these challenges. I will start with a general overview of the experimental landscape, and then focus on our new experimental effort, the Radar Echo Telescope (RET), which uses well-known radar technology to attempt detection of the cascade produced by these UHE neutrinos as they interact in polar ice. I will discuss the theory and storied history of the radar echo method, and recent experimental work including our summer 2023 deployment of a prototype detector. I will conclude with a discussion of the UHE neutrino landscape in the near future, and the exciting possibilities of complementary measurements of the UHE neutrino sky.
Host: Albrecht Karle
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Astronomy Colloquium
Dancing with the stars: next generation models of binary star systems
Time: 3:30 pm - 4:30 pm
Place: 4421 Sterling Hall
Speaker: Meng Sun, Northwestern University
Abstract: Stars serve as the foundational components of astrophysics, with approximately half of them existing in binary systems. Understanding the evolution of these binaries is crucial for understanding mysterious phenomena from the existence of blue straggler stars to the diversity of explosive transients, to black-hole and neutron-star mergers. Modeling these observables needs state-of-the-art modeling of stars and their interactions. An exciting new modeling paradigm is exemplified in POSYDON, a cutting-edge publicly available binary population synthesis code, employs detailed stellar structure and binary simulations from MESA. The code balances both speed and accuracy, providing the best of both worlds and better serving the gravitational wave data analysis. In this presentation, I also delve into how binary stars are modeled in this framework and discuss key mechanisms in developing the new version of POSYDON: wind Roche-lobe overflow and the impact of magnetic braking on angular momentum evolution in binaries.
Host: Ke Zhang
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