Optical Nano-science Research Section

概要

We are engaged in fundamental and applied research of nano-materials from a viewpoint of optics
and material science. Our research aims to explore
new physical and chemical phenomena leading to the
applications of novel nano-materials including carbon
nanotubes, layered transition metal dichalcogenides,
perovskites for the efficient utilization of light energy
and the development of future optoelectronic devices
with ultra-low energy consumption. The followings
are main the research achievements in the year of 2022.
1. Valley Relaxation of the Moiré Excitons in a
WSe2/MoSe2 Heterobilayer
Due to their unusual physical properties and ability
to function as extreme two-dimensional (2D) systems,
atomically thin materials such as graphene and semiconducting transition-metal dichalcogenides (TMDs)
and their van der Waals (vdW) heterostructures have
gained increasing attention. The physical properties of
atomically thin materials originating from a particular
atomic arrangement are significantly altered by
emerging moiré superlattices made up of lattice- or angular-mismatched vdW heterostructures. The moiré
superlattice is gaining attention for its ability to engineer optically excited, tightly bound electron-hole
pairs (excitons) and can result in exciton trapping
through in-plane periodic moiré potentials in twisted
semiconducting TMDs heterobilayers. The quantum
confined zero-dimensional (0D) as a two-level system
created by the moiré exciton trapped in the moiré potentials is encouraging for the development of quantum optics and quantum information processes.
The confinement of moiré potential of exciton alters
the optical characteristics of the system. Under lowexcitation power density conditions, the moiré exciton
results in the appearance of sharp peaks in the lowtemperature photoluminescence (PL) spectrum. Additionally, the moiré pattern (atomic registry) has a significant impact on the optical selection rule of the exciton. The intrinsic valley degrees of freedom control
the optical properties of monolayer TMDs. The K and
-K valleys at the edge of the Brillouin zone are inequivalent but energetically degenerate due to the
strong spin-orbit interaction and lack of inversion
symmetry. ...