Emergent Spectroscopy Research Unit

Principal Investigator

PI Name Youtarou Takahashi
Degree Ph.D.
Title Unit Leader
Brief Resume
2007Ph.D., The University of Tokyo
2007Researcher, Tokura Multiferroic Project, ERATO, Japan Science and Technology Agency
2011Lecturer, Quantum-Phase Electronics Center, School of Engineering, The University of Tokyo
2014Associate Professor, Quantum-Phase Electronics Center, School of Engineering, The University of Tokyo
2014Unit Leader, Emergent Spectroscopy Research Unit, RIKEN Center for Emergent Matter Science (-present)
2016Associate Professor, Quantum-Phase Electronics Center, School of Engineering, The University of Tokyo (-present)


Light-matter interaction has been a fundamental issue for the condensed matter physics. Optical spectroscopy plays an important role for the various researches, and the emergent phenomena in condensed matter provide novel optical responses. Our team focuses on the light-matter interaction on the strongly correlated electron systems as listed below. (1) Magnetoelectric optical effect driven by the cross-coupling between the magnetism and dielectric properties in matter. (2) Optical control of the magnetism and dielectric properties. (3) Novel optical responses derived from the topology in condensed matter. We are pushing forward scientific and technological developments with these researches.

Research Fields

Physics, Material science


Strongly correlated electron system
Terahertz spectroscopy
Ultrafast spectroscopy
Non-reciprocal effect


Magnetoelectric optical effect with electromagnons in helimagnet

Multiferroics, in which the magnetic and the dielectric properties of matter are strongly coupled with each other, has been attracting much attention because of the discovery of the ferroelectricity driven by the particular spin orders.  Although the light is composed of the oscillating electric and magnetic field, one of them is responsible for the optical response in general.  Since the multiferroics exhibits the cross-coupled character, such materials has been expected to possess the composite excitation of the magnetic and the dielectric responses.  We demonstrated the ubiquitous presence of the magnetoelectric resonance with electromagnons, which is magnon excitation endowed with the electric transition dipole moment, in helimagnet.  The electromagnon always shows the optical magnetoelectric effect, which can be observed as the nonreciprocal directional dichroism, in which the optical response changes with the reversal of the propagation vector of light.  We observed gigantic optical magnetoelectric effect on the resonance of the electromagnon, as large as 1 in the imaginary part of the refractive index.

Electromagnon is active for both electric and magnetic field of the light, results in the directional dichroism.


Youtarou Takahashi

Unit Leader youtarou.takahashi[at]riken.jp R

Yoshihiro Okamura

Visiting Scientist


  • Dec 08, 2017 RIKEN RESEARCH Solar cells with a quantum shift
    A quantum-mechanical way of generating photocurrents may help solar devices overcome existing inefficiencies
  • Oct 17, 2014 RIKEN RESEARCH Light finds a one-way street
    A multiferroic material displays a novel spin structure that allows light to travel in only one direction


The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 Japan