Press Releases
Sep. 16, 2009

Photo-detection of the quantum Hall effect proposed

  • Hideo Aoki (Professor, Department of Physics, The University of Tokyo)
  • Takahiro Morimoto (First year graduate student in doctor’s course)

"Quantum Hall effect" is one of the central subjects in the condensed-matter physics, and has received Nobel prizes in physics twice since its discovery in the 1980's. The effect is also relevant to everyday life, since the quantum Hall effect has become the standard of electrical resistance. In the quantum Hall effect, electrons moving in a two-dimensional space, as they do in key devices in digital watches or digital cameras, exhibit Hall conduction (current flowing perpendicular to the applied electric field) when a magnetic field is applied, where the conductivity is quantized into integer multiples of e2/h (e: the electric charge of an electron, h : Planck's constant). So far this has only been considered for static (DC) conductions, but our team (Morimoto, Aoki and Professor Yasuhiro Hatsugai of the University of Tsukuba) has proposed that when we shine a strong laser light to the sample we should have an "optical Hall effect", a novel concept, where the optical Hall response retains, surprisingly, step-like structures (Fig. 1). The relevant photon energy is THz, the energy range of very rapidly advancing optical technology. We have also predicted an even more peculiar optical Hall effect, as observable from a Faraday rotation of polarized lights (Fig. 2), in "graphene", a two-dimensional sheet of carbon atoms which is now one of the hottest topics in both condensed-matter physics as a "neutrino in pencil" and in applied physics as a post-silicon material. The present work gives a prospect of static quantum effects evolving into optical properties. The work has been in part supported by a fund from MEXT.

Paper information

Physical Review Letters 103, 116803 (2009) (published on 11th September, 2009).
"Optical Hall conductivity in ordinary and graphene QHE systems"
Takahiro Morimoto, Yasuhiro Hatsugai and Hideo Aoki

Figure 1

Fig. 1. Optical Hall conductivity σxy(vertical axis) in graphene plotted against energy εF (horizontal axis) and frequency of the light ω(depth axis). In the color coded plot, each region of the same color corresponds to a Hall step.

Figure 2

Fig. 2. Optical Hall effect as detected by Faraday effect, where a polarized light incident on graphene rotates its polarization as it is transmitted.