****NON-TECHNICAL ABSTRACT**** Charge-density-wave (CDW) conductors are among the most remarkable electronic materials ever discovered. They exhibit collective charge transport, nonlinear electronic conduction, coherent voltage oscillations, a low-temperature glass phase and gigantic dielectric constants. They provide a nearly ideal model experimental system for studying the static and dynamic properties of disordered elastic media, providing a tractable way station between simple mechanical oscillators and the complexity of fully developed turbulence. This individual investigator project will explore the electronic properties and possible applications of microfabricated CDW devices, and the complex dynamical response of these devices. The project is part of a broader program that has yielded several patent applications and a commercial product used around the world, and that provides excellent training to graduate students for careers in research and development. Complimentary activities are attempting to address major problems in the STEM pipeline. These include developing methods and curricula for teaching physics to diverse audiences, developing methods and materials for recruiting and retaining students in high school and college physics and, with PhysTEC support, recruiting and training more high school physics teachers.
Quasi-one-dimensional conductors exhibiting collective charge transport by sliding charge (or spin) density waves (CDW) are among the richest systems in condensed matter physics. This project will address two broad classes of problems using a combination of materials synthesis, microfabrication and transport measurements. The first class involves the meso- and nano-scale physics of quasi-one-dimensional conductors and devices that incorporate them. Experiments on the physics of charge injection, of nanowires and of metastability with potential applications in memory devices are enabled by fabrication processes developed in the previous funding period. The second class addresses the collective pinning and dynamics of the disordered CDW, a focus of renewed interest as theoretical methods developed to explain other disordered elastic objects are being used to address the full richness of CDW systems. The project is part of a broader program that has yielded several patent applications and a commercial product used around the world, and that provides excellent training to graduate students for careers in research and development.
This project has focused on the physics of charge-density-wave conductors. These materials exhibit a remarkable array of electrical transport phenomena, including voltage oscillations in response to applied dc currents and a host of electrical memory effects. The underlying physics has connections with those of superconducting systems, earthquakes, and liquids spreading across surfaces. The project has involved development of novel high performance electronics and microfabricated samples that have allowed unprecedented study of the complex spatiotemporal dynamics of CDWs, and in particular of the complex interplay between disorder, elasticity, and longitudinal and shear plasticity. This project has also involved study of the physics of cryopreservation, and specifically on how solutes affect the nucleation and growth of ice during slow and rapid cooling of aqueous solutions. The results provide new and fundamental insight into how cryoprotectants work, and have major consequences for vitrification approaches to biological cryopreservation. During the course of this project, the PI established and has continued to run and expand a program designed to give undergraduates in STEM disciplines a structured introduction to teaching and to teaching careers, especially at the high school level, in attempt to address critical STEM teacher shortages at the middle and high school level. The program partners undergraduates with graduate teaching assistants in the cofacilitation of cooperative problem solving sessions, labs and study sessions in introductory physics courses. All program participants take a seminar course in key ideas in physics teaching and learning, taught by a master high school physics teacher. All are assigned a local high school science teacher as a mentor, who reviews and critiques videos of their classroom performance and answers questions about teaching careers. Several graduates of the program have gone on to become high school physics and chemistry teachers. The program currently engages 55 students per semester and services six introductory physics courses with total enrollment of roughly 1200 students per semester.
