MRI: Acquisition of a High Energy Resolution Angle Resolved SpinPolarized Photoemission Instrument

University Of Missouri-Kansas City, Columbia MO

Investigators

Abstract

Technical Summary: The combination of high angular- and energy-resolution with spin resolution, using spin polarized photoemission spectroscopy, is crucial for reaching a level of understanding of the electronic structure of magnetic and superconducting solids not possible with other techniques (e.g., x-ray magnetic circular dichroism, spin-polarized neutron scattering). Usually to obtain high performance in energy and angular resolution, spin information is sacrificed (e.g., by spin-integrated angle-resolved photoemission spectroscopy); conversely, spin analysis (e.g., using spin-polarized photoemission spectroscopy) is usually carried out at lower energy and angular resolution. The high transmission of the new generation of electron energy analyzers and the high fluxes available from insertion devices at modern Light Sources enables count rate-to-resolution limitations to be overcome. This project aims to acquire an instrument that combines the best possible throughput in addition to both energy and momentum resolution with spin analysis. The present NSLS (National Synchrotron Light Source) or future NSLS II undulator to which this analyzer will be attached, as well as focusing optics (micro spot size), large flux (order of magnitude increase over best known) and energy range (10 to 4500 eV) combined, add unprecedented capabilities to the acquisition instrument and resultant spin-resolved electronic structure determinations. For this instrument alone at beamline U5UA of the NSLS, it will be unique within North America (±38º angular mode, with <6 meV spin resolved photoelectron resolution). When coupled to the upgraded NSLS II, this instrument will be unique within the world, with the ability to probe physically small (<5 microns) magnetic features over a large energy range (providing elemental specificity) with both high energy and angular resolution. The basic science extracted from this instrument will have direct impact in advancing lightweight magnets, next generation superconductors and in developing new mechanisms for future magnetoelectronic devices. As the instrument is housed at a federal laboratory with established methods for optimizing user beamtime, the largest cross section of science and scientists will gain access to these unique capabilities. Layman Summary: Major advances in understanding superconducting and magnetic materials require understanding their spin-polarized electronic structure. 'Spin' is a quantum mechanical property of electrons that endows an individual magnetic moment while the 'electronic structure' can describe how insulating or metallic a solid is and can provide clues as to why the solid exhibits certain physical, optical, electrical, or chemical properties. This project aims to acquire a state-of-the-art instrument that can directly probe how tightly bound electrons are to a solid and how the electron spins communicate amongst each other, hence giving information about the spin polarized electronic structure. This instrument (a spin-resolved electron energy analyzer) will be coupled to a synchrotron radiation source, where 'synchrotrons' are specialized light sources that are advantageous because of the large energy (or wavelength) ranges they provide with a large number of photons per area per time (i.e., high intensity) and because they are intellectual and physical centers of confluence where the greatest number of people may have access to such a capability (instrument + synchrotron). The information gathered with this instrument will help in the advance of materials used in next-generation devices, such as memory, storage, and processing components. Lastly, as part of this project, beamtime proposals and project applications will be developed with the Faculty and Student Teams (FaST) Program at Brookhaven National Laboratory, where each summer, one faculty member and up to three undergraduates will perform studies using the requested instrument. The FaST program separately provides both travel and housing funds, as well as a stipend to both the students and faculty during the ten weeks in summer, making this a very realistic program for obtaining new users from institutions that would otherwise not have had this opportunity.