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 unit 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.
Magnetoelectric optical effect with electromagnons in helimagnet
Helical spin orders exhibit the magnetically induced ferroelectricity, resulting in the concept of multiferroics with strong magnetoelectric coupling. In addition to the ferroelectric polarization, the helical spin orders possess the chirality; the right-handed and left-handed spin habits are distinguished in terms of chirality. The strong magnetoelectric coupling generates the novel spin excitation referred to as electromagnon, which is the magnon endowed with the electric activity, in terahertz region. We clarified that the strong magnetoelectric coupling of the electromagnon resonance causes the nonreciprocal optical effect in general. We also demonstrated the electric field control of chirality by using the helical spin order with ferroelectricity and chirality. On the electromagnon resonance, the reversal of the natural optical activity, which is most fundamental nature of chiral matter, is observed. The control of optical activity may lead to the novel chiral optics.
Control of natural optical activity induced by helical spin-order
