Spin- and momentum resolved photoemission

Fig. 1: The working principle of our spin resolved momentum microscope. The momentum distribution of the photoelectrons emitted from the sample is collected by a photoelectron microscope (PEEM) column. For energy selection, we use an aberration corrected electrostatic energy filter. At the exit of the imaging energy filter, momentum images are recorded on one of two detector branches, for spin-integrated or spin-resolved images, respectively.

A central concept in solid state physics is the description of the degrees of freedom of the electrons in a band structure of independent particles. The band structure describes the dispersion of different electronic states by the relation of the energy E as a function of the crystal momentum k. In general, the electronic bands of electrons with opposite spin ("up" or "down") are not identical. For instance in ferromagnets, the exchange interaction leads to a macroscopically aligned magnetization, and a splitting of bands with different spin in energy.

We investigate the spin resolved band structure by using photoemission. Fig. 1 shows a scheme of the experimental setup we use. The momentum microscope allows to collect photoelectrons that are emitted from the sample in all possible directions, i.e. into the full k|| momentum space, into a single image recorded by a CCD camera. Fig. 2 shows the example of the band structure of copper measured in the momentum microscope.

Our work can be divided into the following sections:
1. Spin resolved photoelectron microscopy
2. Mapping of the spin resolved band structure of ultra thin ferromagnetic films

Fig. 2: Photoemission experiment showing th band structure of copper. Photoelectrons were excited by illumination with He-I radiation (21.2eV photon energy). left: measured dispersion of the sp- and d-bands of copper (E vs. k||). right: Photoelectron momentum distribution at the Fermi surface (top) and at the onset of d-bands (bottom).