| 研究実績の概要 |
This year, we are interested in such intrinsic second order signal generation in other different materials and also start to work on other topics. For example, in transport measurement, the symmetry allows that the second harmonic voltage could appear in transvers direction, and one of the microscopically contribution is from both the dispersion of band structure at the Fermi energy and the Berry curvature distribution in the momentum space. Such measurement of second harmonic voltage and also the symmetry engineering will be our recent goal in the near future.
In order to make graphene heterostructure, we have further developed our transfer technique and introduce dry pickup method in our lab. Furthermore, we carry out the polarized Raman spectrum and so that we could know the orientation of both materials and then precisely control the twisted angle. After optimize the fabrication process of graphene heterostructure device, we have finally achieve large size (tens micrometer size) high quality graphene interface, which can be measured by both transport and optics.
Finally, we observed pseudo magnetic field effect in graphene heterostructure, the shifted and thus duplicated the Landau fan diagram of pristine graphene into two branches, governed by time reversal symmetry. Second, we observed pretty good quantum Hall state and good edge transport phenomena. Third, we observed nonlinear signal in transverse direction without external magnetic field, originated from Berry curvature distribution at the Fermi surface in the momentum space.
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