Study of the Fermi Surface of Bismuth Nanowires

Howard University, Washington DC

Investigators

Abstract

*** NONTECHNICAL ABSTRACT *** This Individual Investigator Award supports a study of bismuth nanowires aimed at understanding their electronic transport and thermoelectric properties. Because of the small effective mass of the charge carriers, the electronic transport in bismuth nanowires is strongly quantum-mechanical in nature. Apart from interesting quantum effects, bismuth nanowires are also interesting for some applications. For example, bulk bismuth is a very efficient thermoelectric material, which can provide a solid state cooling method that involves neither mechanical parts that wear down nor fluorocarbons that damage the environment. Theoretical models of electronic transport predict that the cooling efficiency of fine bismuth nanowires is substantially enhanced over that of the bulk material. Thus, there is a potential for developing a practical cooling method for high-temperature superconductor applications and miniature refrigerators. The work supported by this award involves the synthesis of small diameter (few tens of a nanometer) bismuth wires and measurements of the electrical resistance and response to high magnetic fields at very low temperatures. The experimental results will be compared with theoretical predictions. Researchers and students from Howard University and Boston College participate collaboratively in carrying out this research. The project will train students at doctoral and undergraduate level in nanoscience and technology, thus preparing them for careers in academe, industry, or government. Strong African-American student participation is anticipated. *** TECHNICAL ABSTRACT *** This project investigates the evolution of the Fermi surface of bismuth from bulk semimetal to quantum nanowire. Theoretically, for wire diameters near 60 nm, quantum confinement causes a semimetal-semiconductor transition to a state of large thermopower. However, surface states may mask this transition. Also, it has been predicted that for a strictly one-dimensional interacting electronic system the Fermi liquid description of electrons and holes does not apply, and the excitation spectrum of one-dimensional systems (Luttinger liquid) consists of charge and spin density waves. The goal of this research project is to understand these phenomena through an experimental study of electronic transport, thermoelectricity and magnetism down to very low temperatures (0.3 K) and for magnetic fields up to 47 T. Since these nanowires display Shubnikov-de Haas and de Haas-van Alphen oscillations, which enable direct study of the Fermi surface of bulk conductors, this project aims at extending the experimental methods and the physical picture of Landau states to low-dimensional conductors. This project is a collaboration between Howard University and Boston College and involves training of graduate and undergraduate students. A major focus of the student training is to offer career advancement opportunities for several African-American students at Howard University.