Initial state symmetries from polarization effects in angular resolved photoemission

Abstract

Polarization dependences are present in all angle-resolved photo-emission spectra. When the spectra are obtained with a polarized source such as synchrotron radiation, the effects are manifest. The effects make it possible to use polarization-dependent angle-resolved photoemission UV spectroscopy (PARUPS) to infer initial state symmetry of the electronic states being excited. The ability to measure the initial state symmetry is a newly developed feature of photoemission whose importance parallels that of measuring the surface component of the momentum. The symmetry rules are obtained by examining the symmetry properties of the dipole matrix element in combination with the general result that J. Hermanson has shown for the symmetry of the final states observed in photoemission, i.e. the photoemission experiment only detects even final states when one observes normal emission or emission in a mirror plane. An overview of several applications of these measurement procedures is given for surface state systems and chemisorbed systems. First one wants to measure the initial state symmetry to obtain the properties of the specific system to be measured. For example, CO on nickel, oxygen on nickel or aluminum. Secondly, the polarization dependence can be used to sort out photemission features which are energetically overlapped in a spectrum obtained with mixed polarization.