Development of a Spin Polarized Inverse Photoemission Spectrometer

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This work is concerned with building a new facility to study the spin-polarized unoccupied bands of ferromagnetic thin films and surfaces and Mott-Hubbard insulators. This facility will permit, in conjunction with existing spin polarized photoemission facilities, to identify the exchange splitting of large local moment systems where spin mixing rather than exchange splitting collapse occurs. As with ferromagnetic systems, we also plan, in the case of systems exhibiting Mott-Hubbard transitions, to identify the upper Hubbard band in systems where the Hubbard bands exhibit ferromagnetic (as opposed to antiferromagnetic) ordering. By building this facility, the characterization of not only the occupied band structure (the occupied density of states) but the unoccupied band structure (the unoccupied density of states) is possible. This proposal is based upon existing expertise of five research groups in photoemission, spin- polarized photoemission, inverse photoemission, spin-polarized electron sources, and magnetism. %%% Photoemission, has been the spectroscopy of choice in characterizing electronic structure. The use of polarized light in angle-resolved photoemission studies has made the identification of electronic bands through symmetry selection rules possible, greatly enhancing the technique. These techniques probe the occupied part of the band structure: the valence bands of semiconductors or occupied states of metals and condensed matter systems. More recently, inverse photoemission studies have found a unique role for exploring the conduction band of semiconductors or the unoccupied states of metals and condensed matter systems. Spin-resolved photoemission and spin-resolved inverse photoemission have greatly enhanced the study of electronic structure; particularly in the case of systems with spin-ordered bands, such as ferromagnetic systems. We propose to complement our existing facilities with spin resolved inverse photoemission capability in order to chara cterize both occupied and unoccupied parts of the band structure. This combination of facilities will substantially enhance the ability to investigate magnetic thin films and surfaces and nonmetal to metal transitions. It is this combination of techniques at a single center which would be unmatched by any other facility in the world.