February 21, 2020

Cyrus Dreyer: Understanding solids with supercomputers, many electrons at a time

According to visionary American physicist Richard Feynman:

“If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis that all things are made of atoms — little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another.”

The properties of the materials that make up the world around us are governed by how these atoms attract and repel each other. For example, whether a solid is hard and translucent like diamond, or soft and opaque like graphite; whether a material conducts electricity and heat like copper, or prevents the flow of electricity and heat like rubber; whether a material can be used in computer chips, like silicon; or whether a drug like aspirin will mitigate a fever. The outer “valence” electrons, i.e., those furthest from the atomic nuclei containing the protons and neutrons, play the most important role in these interatomic interactions, and therefore the properties of the materials made of the atoms. All of our technology is based on our ability to design and engineer materials, and thus it is crucial to be able to understand how the valence electrons in a material interact.

This turns out to be a very difficult problem, one that has challenged scientists for a century. For one thing, electrons are small, and thus governed by the weird properties of quantum mechanics. Also, there are a lot of them in a given material: there are more electrons in the atoms that make up a paper clip than there are stars in the universe. In this talk I will describe a particular approach to tackling the “many electron problem”, known as Density Functional Theory, which, combined with the most powerful supercomputers in the world, has revolutionized our ability to describe and predict the properties of materials. I will give a variety of examples of how this knowledge of materials can be used to develop novel electronic devices for modern technology. Cyrus Dreyer earned his B.S. from the University of Virginia, Ph.D. from the University of California, Santa Barbara, and then was a postdoctoral associate at Rutgers University. He is now an assistant professor at Stony Brook University in the department of Physics and Astronomy and an affiliate associate research scientist at the Center for Computational Quantum Physics at the Flatiron Institute in New York City. His research interests involve developing and implementing computational techniques based on density functional theory to explore the properties of electronic materials.

March 13, 2020

Derek Teaney: Having fun with quark gluon plasma

First I will describe what is the Quark-Gluon Plasma (QGP), which serves as a prototype for the types of plasmas that existed during the first microseconds after the big-bang. The QGP has several unique features: it is an ultra-relativistic plasma where radiation plays an important role and it is very non-linear (non-abelian). Finally, I will describe a sequence of experiments at Brookhaven's Relativistic Heavy Ion Collider (RHIC) and CERN's Large Hadron Collider (LHC) which have recreated the Quark-Gluon-Plasma in the lab (and studied its properties) by colliding large nuclei at high energies.

Derek Teaney received his undergraduate degree from Yale in 1995 and his doctoral degree from Stony Brook in 2001. After holding several posts at Brookhaven National Lab and Arkansas State University, Professor Teaney, returned to Stony Brook in 2007 as an assistant professor and was subsequently promoted to associate professor in 2013. He enjoys teaching at variety of levels.

April 10, 2020

Peter Chupas: TBA