Room 10.01, Bldg. 30.23 CS and Zoom
University of Tokyo
Quantum materials with broken inversion symmetry carry a potential for novel quadratic optical responses, for instance, photovoltaic effect and second harmonic generation. These nonlinear optical responses have attracted much attention in the aspect of an application for the next-generation optical-electronic devices, such as unconventional solar cells and optical sensors. However, previous studies on nonlinear optical responses mainly focused on systems of noninteracting electrons, and effects from strongly correlated systems have not been fully explored so far despite the possibility of enhanced and controlled responses through the multi-degree of freedom of electrons.
In this study, we focus on noncentrosymmetric magnets as an example among a variety of strongly correlated materials. Based on the diagrammatic method, we theoretically investigate linear and nonlinear optical conductivities on the two types of one-dimensional noncentrosymmetric magnetic systems. First, we show the photovoltaic effect and second harmonic generation in electrons coupled to a chiral magnet with the Dzyaloshinskii-Moriya interaction. We find that these quadratic responses in the chiral magnets can be colossal and vary drastically depending on the frequency of the incident lights, the magnetization, and the spin-charge coupling . Second, we also study the photovoltaic effect in a cycloidal magnet with alternating coupling constants. We find that such spin systems without spatial inversion symmetry support the shift current response through magnon excitations under the strong spin-charge coupling . Since the present mechanisms do not require the spin-orbit coupling, which is small and usually suppresses the optical responses, such responses have the potential to exhibit large nonlinear functionality.
 S. Okumura, T. Moritomo, Y. Kato, and Y. Motome, Phys. Rev. B 104, L180407 (2021).
 T. Morimoto, S. Kitamura, and S. Okumura, Phys. Rev. B 104, 075139 (2021).