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 74.4: Hauptvortrag
Mittwoch, 18. März 2015, 16:45–17:15, H 1012
Ultrafast control of the exchange interaction with electric fields — •Johan H. Mentink — Max Planck Research Department for Structural Dynamics, University of Hamburg-CFEL, 22761 Hamburg, Germany — Radboud University Nijmegen, Institute for Molecules and Materials, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
The strongest interaction between microscopic spins in magnetic materials is the exchange interaction Jex. Therefore, ultrafast control of Jex keeps the promise to control spins on ultimately fast timescales, potentially bypassing fundamental speed limits for the control of magnetism with magnetic fields. In this talk we provide theoretical evidence that the exchange interaction can be manipulated on ultrashort timescales by strong electric field pulses. Focusing on the prototype Mott-Hubbard insulator, we find very different effects for resonant and off-resonant photo-excitation. In the former case, the electron distribution is changed and the subsequent relaxation of photo-excited carriers causes an ultrafast reduction of Jex. Conversely, off-resonant driving allows for an ultrafast and reversible control of Jex, i.e., it is active while the field is on, but leaves the electronic state unexcited after the pulse is switched off. In the regime of weak-driving strength the modification of Jex is proportional to the intensity of the electric field and we find that Jex can be enhanced and reduced for frequencies below and above gap, respectively. Furthermore, for strong driving even the sign of the exchange interaction can be reversed and we show that this causes time reversal of the associated quantum spin dynamics.