Origin and stability of highly spin polarized surface resonances

• Applicant: Professor Dr. Martin Jourdan
• Subject Area: Experimental Condensed Matter Physics ; Theoretical Condensed Matter Physics
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 272511961

The magnitude of the spin polarization of ferromagnetic materials at room temperature is a key property for spintronics. However, for most applications it is not the bulk, but the surface or interface of the material, which is relevant. Investigating the Heusler compound Co2MnSi we recently observed a high spin polarization, which is related to a stable surface resonance in the majority band extending deep into the bulk.Here we want to investigate the physical origin of such highly spin polarized surface resonances. This study includes experimental and theoretical investigations of different Heusler and related compounds and surface orientations. In particular, the question whether a half metallic bulk band structure is a necessary precondition for the appearance of a 100% spin-polarized surface resonance should be answered. Considering potential applications it is of major importance whether the high spin polarization due to a surface resonance is conserved, if the free surface is replaced by an interface with an insulator or metal.The main experimental method for the investigation of the surface and interface states will be in-situ spin resolved photoelectron spectroscopy (SR-UPS) and for a larger probing depth spin integrated high energy x-ray photoemission spectroscopy (HAXPES). The results will be interpreted in comparison with first-principles band structure and photoemission calculations which consider all relativistic, surface and high energy effects. Special emphasize will be put on electronic correlations as well as finite temperature effects using state of the art approaches mostly developed by the applicants concerning surface, temperature and high-energy aspects.

• DFG Programme: Research Grants