Colloquium: Dr. Elijah Flenner, Research Scientist at Colorado State University

On Friday, October 14 at 2:00 PICS will host an in-person colloquium featuring Elijah Flenner, Research Scientist II at Colorado State University

Title: “Sound Attenuation and the Vibrational Properties of Glasses”

Abstract: Understanding of the universal low-temperature properties of glasses and why they differ from their crystalline counterparts requires the understanding of the vibrational properties of glasses. Due to recent advances of computational techniques, we are now able to study simulated glasses with a wide range of vibrational properties, which is essential to understanding their role in the low-temperature properties of glasses. In this talk I will discuss the stability dependence of the vibrational modes of glasses ranging from poorly annealed to exceptionally stable. Our most stable glasses are comparable to exceptionally-stable, vapor- deposited laboratory glasses. We find that the density of quasi-localized, low-frequency modes decrease quickly with increasing stability and the density of these modes are correlated with sound attenuation in the harmonic approximation. We use a recently developed theory that very accurately reproduces the low-frequency sound attenuation to examine the relationship between the vibrational modes and sound attenuation. This theory indicates that the non- affine forces, which are responsible for the renormalization of the speed of sound in amorphous solids, is responsible for sound attenuation. Surprisingly, we find that the low- frequency, quasi-localized modes make a relatively small contribution to the sound attenuation coefficient compared to the extended, low-frequency modes. I will conclude by discussing recent attempts at identifying regions of the glass that play an enhanced role in sound attenuation, if they exist.

Bio: Dr. Elijah Flenner is a Research Scientist in the Department of Chemistry (2013 to present) at Colorado State University. He obtained his B.S. degree in 1997 in Physics and Mathematics from University of Missouri-Columbia and his Ph.D. in Physics in 2003 from Colorado State University. After graduating from Colorado State University, he started his postdoctoral work with Dr. Grzegorz Szamel at Colorado State University, where Dr. Flenner started his research into glasses with a focus on dynamic heterogeneity. In 2006 he started a second post-doctorate position working on modeling of organ printing with Dr. Kosztin at University of Missouri- Columbia. After two years at the University of Missouri, Dr. Flenner returned to CSU and started a new position as a Research Scientist. At Colorado State University he continued working on glasses and made contributions to the study of heterogeneous dynamics in glass forming liquids. More recently Dr. Flenner has utilized a new Monte Carlo algorithm to examine the vibrational properties of glasses and how these properties are related to the universal, anomalous properties of glasses. Additionally, he studies the behavior of model active matter systems, systems that consume energy in order to move. These systems often exhibit persistent, directional motion that results in behavior very different from passive systems. His recent work on active matter systems includes examining the role of velocity correlations, which have no counterpart in passive systems, and how the activity influences the glass transition.