Quasi-1-D Molecular Organic Conductors: Experiment and Simulation

Boston College, Chestnut Hill MA

Investigators

Abstract

NON-TECHNICAL: Everything in our everyday experience with electricity and electronics, from the current running through the toaster oven to the entire information technology revolution, involves electrons that don't "talk" to each other. We have learned to manipulate the electron's charge to the extent we have because we understand how they can be considered non-interacting in spite of the opposites attract, likes repel dictum. Magnetism and superconductivity are spectacular exceptions to this nontalking state, but there are others, and there is much more to learn about the electron. Much of what is new is being found when electron motion is severely confined. We already know that new phenomena arise when strict planar geometry is imposed (two-dimensionality). Realization of this condition in modern semiconducting materials led directly to the discoveries of the integer and fractional quantized Hall effects. The former involves electrons that hardly talk to each other, while for the latter, they are intimately and exquisitely engaged. The present project deals with the nature of the electron when its motion is further confined, to one dimension. There are certain organic and molecular materials that are quite good electrical conductors, and whose structural characteristics are such that the electron motion is very nearly one-dimensional. Again, as a result of geometric constrictions, and the concomitant increase in the importance of quantum mechanical effects on small size scales, new phenomena are arising, especially in strong magnetic fields. This project investigates the behavior of electrons in one-dimensional materials, in particular the nature of the recently-discovered interference-commensurate magnetoresistance oscillation phenomena discovered by the project PI. Knowledge gained from this study will be found to be of much use by technologists wishing to devise nanoscale electronic and electromagnetic structures, for example using carbon nanotubes, where one-dimensional effects will dominate. The project will promote student learning and discovery of the physics of novel materials at several levels, high school, undergraduate, and graduate, through summer internships, fellowships and workshops. TECHNICAL: This individual investigator award supports an experimental project to investigate low-dimensional conductors and superconductors. One goal of this project is to determine the origin of angular magnetoresistance oscillations in quasi-one-dimensional organic metals. Recent experiment and theory suggest a new type of macroscopic quantum effect, interference commensurate oscillations, or perhaps this is a new manifestation of a known effect. Angle-dependent magnetotransport measurements in the highest attainable fields (45 tesla at BC, 60 tesla at NHMFL) will be used to examine in detail the 1D-to-2D dimensional crossover phenomenon seen in TMTSF organic conductors. Also, using nanolithographic and microcantilever techniques, finite size effects, and their impact on spin density waves and spin-triplet superconductivity, will be explored for the first time in these materials. The project will promote student learning and discovery of the physics of novel materials at several levels, high school, undergraduate, and graduate, through summer internships, fellowships and workshops.