Berlin 2015 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 74: Focus Session: Ultra-Fast Magnetism under Electronic Nonequilibrium Conditions (organized by MA)

TT 74.3: Hauptvortrag

Mittwoch, 18. März 2015, 16:15–16:45, H 1012

Laser induced ultrafast demagnetization in solids: a time-dependent density functional theory perspective — •Sangeeta Sharma, J. K. Dewhurst, K. Krieger, P. Elliott, and E. K. U. Gross — Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle, Germany.

Ultrafast manipulation of spins in a controlled manner is a milestone of solid state physics. The motivation for this is to use electronic spin for storing binary data, which can then be optically manipulated using lasers. Recent experiments have demonstrated that demagnetization or spin-reorientation processes can be induced by femtosecond laser pulses. However, we are still far from achieving optimally controlled manipulation of spins required for production of devices. One of the reasons behind this is the lack of full understanding of the phenomena leading to demagnetization.

Time-dependent density functional theory (TDDFT) is a formally exact method for describing the real-time dynamics of electrons under the influence of an external field – for example vector potential of the intense laser pulse. We use spin-resolved TDDFT to study of the process of optical demagnetization. The advantage of such a technique is clear from the fact that it is fully ab-initio in nature. Our analysis shows that the demagnetization occurs as a two step process where first the electrons make transitions to excited states, followed by spin-orbit-mediated spin-flip transitions which lead to a loss of moment. Non-collinearity of the spins does not play significant role in the demagnetization process.