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Events on Thursday, February 16th, 2023

R. G. Herb Condensed Matter Seminar
Strange Metal Behavior in the Hall Coefficient of BaFe2(As,P)2
Time: 10:00 am - 6:00 pm
Place: 5310 Chamberlin
Speaker: Ian Hayes, University of Maryland
Abstract: Even after decades of research on the high-Tc cuprates, several parts of their phase diagrams remain mysterious, especially the normal state above Tc near optimal doping, a region commonly referred to as the strange metal phase. New avenues for studying this physics were opened up by the discovery of the iron-based high-Tc materials, which also exhibit strange metal characteristics, particularly a T-linear resistivity and a roughly 1/T Hall coefficient near optimal doping. In this talk I will present measurements of the Hall coefficient in phosphorous-doped BaFe2As2 in fields of up to 65 tesla, which is enough to suppress superconductivity even at optimal doping. These measurements reveal a striking parallel between the effects of increasing magnetic field and the effects of increasing temperature, a phenomenon that is reminiscent of the field-temperature scaling seen in the resistivity of this compound. This characteristic field dependence allows us to clearly identify the extent of strange metal physics in the entire phosphorous-doping phase diagram. Intriguingly, the presence of strange metal behavior in the Hall coefficient is directly related to the presence of the superconductivity across the phase diagram. I will discuss the implications of these observations for different approaches to the strange metal as well as the opportunities they present for future research.
Host: Victor Brar
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Particle acceleration in astrophysical, magnetized turbulent plasmas
Time: 2:30 pm - 3:30 pm
Place: CH4274/Invite Link Invite Link
Speaker: Martin Lemoine , Institut d’Astrophysique de Paris, CNRS
Abstract: How magnetized turbulent plasmas can accelerate charged particles to high energies represents a long-standing question with far-reaching implications for high-energy and multi-messenger astrophysics. It indeed goes back to the seminal works of Enrico Fermi (1949, 1954) and nowadays, it is commonly invoked to model the generation of non-thermal particle spectra in a broad variety of astrophysical sites, including extreme, relativistic sources. In particular, it has recently been considered as a possible origin for the high-energy neutrinos seen by Ice Cube in the direction of nearby active galactic nuclei. Our understanding of particle acceleration in turbulent plasmas has known substantial progress in recent years, mostly spurred by large-scale, kinetic numerical simulations. This talk will address those developments and discuss a theoretical picture to describe the physics at play, based on non-resonant interactions between particles and velocity structures. This model, which can be seen as a modern implementation of the original Fermi scenario, appears supported by recent numerical simulations of turbulence in the semi- and fully-relativistic regime. It also brings to light an interesting connection between the properties of intermittency of the turbulence and the spectrum of accelerated particles. I will discuss those features then conclude with some possible applications and extensions.
Host: Ellen Zweibel
Presentation: Lemoine_UWM23.pdf
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Physics Majors Fair
Time: 4:30 pm - 5:30 pm
Place: University Ave Lobby and Physics Museum
Speaker: Evan Heintz, Undergraduate Advisor
Abstract: Learn about the Physics major! We'll have faculty and staff on hand who can help you declare your major in Physics and answer any questions you may have about studying undergraduate Physics at UW-Madison.
Host: Evan Heintz
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