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Colossal optical isolator effect driven by spin helix

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Posted August 25, 2014
This news or article is intended for readers with certain scientific or professional knowledge in the field.

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.

When a helical spin structure shows up in matter, the light coming from the left side transmits, but the light coming from the right side is absorbed on the resonance of the electromagnon. © 2014 Youtarou Takahashi.

When a helical spin structure shows up in matter, the light coming from the left side transmits, but the light coming from the right side is absorbed on the resonance of the electromagnon. © 2014 Youtarou Takahashi.

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.

Source: University of Tokyo

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