2019 Fall Graduate Colloquium: Caleb Zavala/William Julius

DateNovember 8, 2019
Time3:35 - 5:00 pm
LocationBaylor Sciences Building, Room E.125
Description
2019 Fall Graduate Colloquium Series



Caleb Zavala


Maximized Electron Interactions at the Magic Angle in Twisted Bilayer Graphene



By stacking two sheets of graphene on top of one another and twisting one layer by a certain angle of a twist about 1.1 degrees called the magic angle, the properties of graphene can be modified and have been shown to have superconductivity phase. At other angles, twisted bilayer graphene has also been shown to have an insulating phase. In this paper, they mapped the atomic-structural scale and electronic properties of twisted bilayer graphene near the magic angle using scanning tunneling microscopy and spectroscopy. While looking at the magic angle and decreasing the twist angles or doping the material, they observed different correlated behavioral proprieties. During their investigation, they found that at the magic angle the ratio of the coulomb interaction to the bandwidth of each individual Van Hove singularities was maximized. From there measurements about the magic angle of twisted bilayer graphene they were able to gain insight about the materials superconducting state.



https://doi.org/10.1038/s41586-019-1431-9




William Julius


A Beginners Guide to Hiding Your Problems

(So long as they have to do with spherically symmetric traversable wormholes)



In 1988, Mike Morris and Kip Thorne Published a paper detailing the mathematics describing a spherically symmetric traversable wormhole. Such a wormhole could, at least in principle, allow an observer to travel between two arbitrarily separated locations in space as fast as they wish. Such a solution does, however, possess some interesting features. One of the more interesting features is that exotic matter (usually in the form of some sort of negative energy density) is required to open and stabilize the throat of the wormhole. This year, Peter Kuhfittig proposed an extension of Morris and Thorne’s construction to a spacetime containing an extra (non-compact) spatial dimension. He showed that such a modification allowed a local observer traversing the wormhole in only our usual four dimensions would be unable to see any negative energy densities. An observer who is able to traverse the extra dimension would be able to see negative energy density, effectively allowing for the negative density needed to stabilize a wormhole to be hidden. Here we will present Morris and Thornes original construction, Kuhfittigs extension to this construction, and third novel extension which makes the extra dimension compact.


https://journals.aps.org/prd/abstract/10.1103/PhysRevD.98.064041; https://aapt.scitation.org/doi/10.1119/1.15620



For more information contact: Dr. Kenneth Park, 254-710-2282
PublisherDepartment of Physics
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