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O: Fachverband Oberflächenphysik
O 86: Ultrafast Surface Dynamics I
O 86.7: Talk
Thursday, March 10, 2016, 16:30–16:45, S052
Hot electron-spin gas drives ultrafast spin density wave transition in Cr — •Chris Nicholson1, Claude Monney2, Robert Carley3, John Bowlan4, Björn Frietsch5, Martin Weinelt5, and Martin Wolf1 — 1Fritz-Haber-Institut, Berlin, Germany — 2University of Zurich, Switzerland — 3European XFEL GmbH, Germany — 4Los Alamos National Laboratory, USA — 5Freie Universitaet Berlin, Berlin, Germany
Transitions to magnetically ordered states are characterised by an order parameter, defined in the (equilibrium) adiabatic limit. However, it is an open question how the order parameter develops on ultrafast timescales following abrupt excitation by an ultrashort laser pulse and if a general description of such ultrafast phase transitions in terms of a theoretically determined order parameter is still possible [1].
We exploit the energy and momentum selectivity of time- and angle-resolved photoemission spectroscopy to address the ultrafast dynamics of the antiferromagnetic SDW photoexcited in epitaxial thin films of chromium. We reveal we are able to quantitatively extract the evolution of the SDW order parameter through the phase transition, which follows the electronic temperature. We observe the complete destruction of antiferromagnetic order on a sub-100fs time scale, which implies that a quasi-equilibrium between electron and spin systems develops on an ultrashort time scale and drives the spin density wave transition in chromium.
[1] P. Beaud et al. Nat. Mater. 13, 1 (2014)