Projekt

The combined measurement of linewidth and lifetime or the decay of quantum beats after coherent excitation of several states in two-photon photoemission delivers insight to quasielastic and inelastic electron scattering processes. On ferromagnetic surfaces these scattering processes include Stoner and electron-magnon excitations and are thus key ingredients for a fundamental understanding of ultrafast magnetization processes. Image-state electrons serve as a well-defined model system for which the distance in front of the surface, i.e. the probed surface area, and the lifetime can be varied about an order of magnitude by choice of the quantum number.
On ferromagnetic surfaces these states are spin split and the lifetime broadening is spin dependent. The states thus reflect the exchange-split bulk-band gap boundaries and allow to study spin-dependent relaxation processes directly from the fs to ps time scale.
Well-ordered itinerant ferromagnetic films are examined as simple model systems. Films of different thicknesses allow to vary the Curie temperature and surface magnetization. The influence of these parameters on spin-dependent inelastic and elastic scattering will be addressed. Measurements below and above the Curie point are used to distinguish between inherent properties of the ferromagnetic and paramagnetic states. This gives the perspective to study ultrafast demagnetization processes driven by femtosecond laser pulses. Corresponding experiments are planned in the second period of this project.