Colossal optical isolator effect driven by spin helix -Demonstration of the new gigahertz and terahertz optical devices-



S. Kibayashi, Y. Takahashi, S. Seki and Y. Tokura



 Y. Takahashi (associate professor, University of Tokyo), S. Kibayashi (graduated student, University of Tokyo), S. Seki (unit leader, CEMS Riken) and Y. Tokura (professor, University of Tokyo, director, CEMS Riken) discovered new optical functionality of the helical spin structure, which differentiates the optical absorption between the counter-propagating light beams.

   They found that the emergence of the electromagnon, which is a kind of collective spin motion, in the frequency range of gigahertz to terahertz, when the helical spin structure shows up.  Due to the presence of the both “magnetism” and “chirality” by the helical spin structure, the electromagnon exhibits the colossal magnetochiral effect, leading to the changes of the extinction coefficient up to 400 % depending on the propagation direction of light beams.

   In the frequency region including the higher gigahertz and terahertz, which is expected for future high capacity communication etc., the optical device is developing.  The current results will be used for the possible optical devices, such as an isolator, and the electrically and magnetically controllable optical elements.