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  • Interferometric control of spin-polarized multi-photon photoemission

    Dr. Aimo Winkelmann
    Max-Planck Institut für Microstructurphysik
    Halle Germany

    Monday, May 19, 2:00 p.m.
    SRC Conference Room

    The interaction of circularly polarized light with electronic states that are influenced by spin-orbit coupling provides a mechanism for selective excitation of spin-polarized electrons in nonmagnetic and magnetic solids.

    This type of interaction bears close analogy to the effect of a magnetic field, and it enables the control of magnetic and other spin-dependent phenomena by optical means on time scales of the order of the applied laser pulse lengths in solids and at solid surfaces.

    From a fundamental point of view, a particularly direct way to study the relevant mechanisms is to optically excite electronic states and then detect spin-polarized photoelectrons emitted from crystal surfaces.

    Using nonlinear photoemission in a pump-probe configuration, one can gain access to the dynamics in the excited states. It is of fundamental interest to elucidate mechanisms by which not only the number but also the spin of the emitted photoelectrons can be influenced by the relative optical phase of two excitation pulses.

    We demonstrate the phase tuning of the spin polarization of photoelectrons emitted in a three-photon process from Cu(001). A phase-shift of Pi between delayed ultrafast circularly polarized light pulses can switch the spin polarization from -20% to +40%.

    In the delay regime of overlapping pulses, we show the dominating role of optical interference effects in determining the spin-polarization. For longer delays, we detect the influence of the coherent material response, manifested in both the final state electron population as well as the final state spin polarization.