2D materials and van der Waals heterostructures

Electronic charge transport in graphene-based nanodevices
Photoresponse in van der Waals 2D materials and heterostructure nanodevices
Our laboratory is able to perform both static (no time-resolved) and dynamic (time-resolved) photocurrent response in graphene and 2D materials devices. This study is related to the novel photodetector, photovoltaic devices, and light-induced photo-switching devices. Using novel microscopy systems combined with ultrafast lasers, we can perform spatially-resolved (~ 1 µm) and time-resolved (~ 100 fs) photoresponse in these devices.

Spintronics and topological insulators

Light-induced manipulation of spin current in spintronic devices
Surface-state and carrier dynamics in topological insulator heterostructures 
The purpose is to investigate new spintronic devices where the spin-polarized current is controlled in the picosecond (1/10¹² s) scale via ultrashort laser pulses. Injection of the time-delayed optical pulses topologically governs the time-resolved spin-polarized photocurrent where the unwanted non-topological thermal current, which is an unsolved problem in the topological insulator-based spintronics, can be suppressed and the spin polarization ratio is aggrandized by inducing the ultrafast bulk-to-surface electron tunneling. Utilizing this unique experimental approach, we can construct a fundamentally different spintronic device based on topological insulators, introducing a breakthrough for realizing the ultrafast photo-controlled spintronic device.

Metamaterials and plasmonic nanostructures

Electrically-controlled metamaterial devices
Fast optical switching of THz waves using metamaterials
For the last few years, we have developed very effective methods in manipulating the THz waves using metamaterial-integrated optoelectronic devices. Active modulation of THz waves was derived by layered composition of graphene metamaterials, where the electrons are migrated from graphene to metamaterials and vice versa. Emphasis should be made on the fact that the electrical and optical manipulation of graphene is at the heart of the THz wave control. By changing the structure of metamaterials, distinguished functionalities of THz optics, refractive index change, and nonlinear wave mixing are demonstrated.