Development of a Spin Polarized Inverse Photoemission Spectrometer

本工作涉及建立一个新的设备来研究铁磁薄膜、表面和莫特-哈伯德绝缘体的自旋极化未占用带。该装置将允许与现有的自旋极化光电发射装置结合，识别发生自旋混合而不是交换分裂坍塌的大局域矩系统的交换分裂。与铁磁系统一样，我们也计划，在系统表现出莫特-哈伯德跃迁的情况下，在哈伯德带表现出铁磁（而不是反铁磁）有序的系统中识别上哈伯德带。通过建立该设施，不仅可以表征已占用的带结构（已占用的态密度），还可以表征未占用的带结构（未占用的态密度）。这一建议是基于现有的五个研究小组在光发射，自旋极化光发射，逆光发射，自旋极化电子源和磁学的专业知识。光电发射，已成为表征电子结构的首选光谱。偏振光在角分辨光电发射研究中的应用，使得通过对称选择规则识别电子带成为可能，大大提高了技术水平。这些技术探测带结构的占据部分：半导体的价带或金属和凝聚态系统的占据态。最近，逆光发射研究在探索半导体的导带或金属和凝聚态系统的未占据状态方面发挥了独特的作用。自旋分辨光发射和自旋分辨逆光发射极大地促进了对电子结构的研究；特别是在具有自旋有序带的系统中，例如铁磁系统。我们建议用自旋分辨逆光电发射能力来补充我们现有的设备，以表征带结构中被占用和未被占用的部分。这种设备的组合将大大提高研究磁性薄膜和表面以及非金属到金属转变的能力。正是在一个中心的这种技术组合，将是世界上任何其他设施无法比拟的。

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.