This experimental project is based on angle resolved photoemission spectroscopy in characterizing the collective excitations of novel materials. The goal of the experiments is to provide critical experimental data to stimulate the development of an analog of the Nambu-Eliashberg theory for momentum resolved spectral function in systems where the quasiparticle excitation is strongly coupled to collective excitations such as phonons or spin fluctuations. Materials of interest are organic conductors and superconductors, doped C60, A15 compounds, BiK BiO3, and high Tc superconductors. Synchrotron radiation and a UV laser will be used as the excitation source. %%% This experimental research project uses the technique of angle resolved photoemission spectroscopy to measure the energy and crystal momentum of characteristic excitations in crystalline specimens of materials of current scientific and technological interest. In this techniq light photons of well specified direction (momentum) and energy (wavelength) fall upon a clean surface of the material of interest. The photoelectric effect leads to emission of electrons from the surface layers of the material. These photoelectrons are detected in such a way that their number, direction and kinetic energy are simultaneously measured. These data, making use of principles of energy and momentum conservation, allow detailed information to be obtained on the collective excitations of the sample. In this work the materials of interest include several different unusual electonic conductor, including films of electronically conducting (alkali- metal doped) carbon-sixty, and several unusual types of superconductors, including a cubic Bismuth Potassium Barium Oxide and high Tc cuprates. The intent of the work is to provide excellent data which may permit theorists to propose and test detailed models for the interaction of electrons in these systems with "collective modes" including lattice vibrations (phonons) and spin waves. It is hoped that a theory analogous to the successful Nambu-Eliashberg theory for electrons and phonons in conventional superconductors such as lead and mercury, might also be found for these more complicated materials of possible technological application. This research project is interdisciplinary in nature and involves graduate students who will be excellently trained to enter positions in industry, government or education. ***
