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Friday, August 22, 2014
Colossal optical isolator effect driven by spin helix
Demonstration of gigahertz and terahertz optical devices
A research group at the University of Tokyo Graduate School of Engineering, consisting of Project Associate Professor Y. Takahashi, graduate student S. Kibayashi and Professor Y. Tokura (concurrently Director, CEMS RIKEN) and CEMS Riken unit leader S. Seki, have discovered a new optical functionality of helical electron spin structures that emerge in matter and by which the optical absorption of counter-propagating light beams is greatly differentiated.
The research group found that the electromagnon, a kind of collective spin motion, emerges in the gigahertz to terahertz frequency range when the helical electron spin structure is present. Due to the helical electron spin structure possessing both “magnetism” and “chirality,” it was further discovered that the electromagnon exhibits a colossal magnetochiral effect. Using this magnetochiral effect, the research group succeeded in altering the extinction coefficient by up to 400 % depending on the propagation direction of light beams.
Research and development of optical devices for control of light (electromagnetic waves) in the frequency region including the higher gigahertz and terahertz, which is expected to be used for applications including future high capacity communications. The current result may be used for the development of optical devices such as isolators that only permit light to pass in one direction and optical devices for the control of light via external electrical and magnetic signals.
S. Kibayashi, Y. Takahashi, S. Seki and Y. Tokura, “Magnetochiral dichroism resonant with electromagnons in a helimagnet”, Nature Communications 5: 4583 Online Edition: 2014/8/1 (Japan time), doi: 10.1038/ncomms5583. Article link