Extra Seminar - Würzburg ToCoTronics Colloquium

Electronic structures of conductive materials can be studied by angle resolved photoelectron spectroscopy (ARPES). However, the sample rotation to cover a wide (k_x,k_y) range induces changes of the selection rules and the probed regions on the surfaces. The low detection efficiency of conventional ARPES also often induces radiation damages spoiling the quality of the obtained results.

To solve these problems, photoelectron momentum microscopy（PMM）was developed. When I met with this approach in the Kirschner Lab at the Max-Planck-Institute for Microstructure Physics, Halle, in 2013, I immediately recognized that this will become the major approach for photoelectron spectroscopy in the 21st century. By the high extraction voltage between the sample surface and the entrance of the PEEM-type objective lens of up to 15 or 20 kV, all photoelectrons emitted into the 2π steradian can be simultaneously recorded by a 2D detector. Then the efficiency becomes orders of magnitude higher than that of conventional ARPES.

In addition, effective spin detection is feasible by use of 2D spin filters at low electron kinetic energies (10.25 and 11.5eV) with a FoM of around 102. Then the spin detection efficiency becomes around 5 million times higher than that of a Fe-O VLEED single channel detector.

Since we have installed a photoelectron momentum microscope (PMM) at UVSOR BL6U+BL7U we can now perform (k_x,k_y,k_z) PMM not only at 68° incidence but also normal incidence. The selection rule dependence of the 3D momentum-resolved electronic structure E_B(k_x,k_y,k_z) is now measurable. Within this year, we will install a Au/Ir(001) spin filter and start spin-polarized PMM (SP-PMM). The sub-μm resolution without any sample movement and radiation damage will provide us useful and reliable information for device development. We will soon start measurements of magnetized samples as well as samples under electric field and uniaxial strain.

On the other hand, non-conductive materials should be studied by other methods. Soft X-ray resonant inelastic scattering (SX-RIXS) combined with theoretical analyses can provide rich information on electronic states. Measurements are feasible under magnetic field, electric field as well as under uniaxial strain. Since this technique is bulk sensitive, focusing of the soft X-ray beam to dimensions smaller than 1μm facilitates reliable measurements.

We would like to mutually collaborate between the static SP-PMM and ToF SP-PMM in the near future to understand the dynamics of spin electronic states.

Reference:
Photoelectron Spectroscopy: Bulk & Surface Electron Structures. Springer Series in Surface Sciences 72, 1-511. 2nd edition(2021). S. Suga, A. Sekiyama and C. Tusche.