Abstract-Tuning terahertz transitions in a double-gated quantum ring

T. P. Collier, V. A. Saroka, and M. E. Portnoi

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.235430

We theoretically investigate the optical functionality of a semiconducting quantum ring manipulated by two electrostatic lateral gates used to induce a double quantum well along the ring. The well parameters and corresponding interlevel spacings, which lie in the THz range, are highly sensitive to the gate voltages. Our analysis shows that selection rules for interlevel dipole transitions, caused by linearly polarized excitations, depend on the polarization vector angle with respect to the gates. In striking difference from the conventional symmetric double well potential, the ring geometry permits polarization-dependent transitions between the ground and second excited states, allowing the use of this structure in a three-level lasing scheme.

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Colossal optical isolator effect driven by spin helix

Demonstration of gigahertz and terahertz optical devices

http://www.u-tokyo.ac.jp/en/utokyo-research/research-news/colossal-optical-isolator-effect-driven-by-spin-helix/

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.

© 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.

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.

Press release

Paper

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

Links

Graduate School of Engineering

Quantum-Phase Electronics Center, Graduate School of Engineering

Department of Applied Physics, Graduate School of Engineering

Takahashi Laboratory, Quantum-Phase Electronics Center, Graduate School of Engineering (Japanese)