Congratulation Dr. Lim for Nanoletter paper accepted recently!
This is work done in collaboration with University of Seoul. We hope to do some high quality work on Terahertz research on carrier dynamics in near future.
Title: Gate-controlled nonlinear conductivity of Dirac Fermion in graphene field-effect transistors measured by terahertz time-domain spectroscopy
Authors: Inhee Maeng, Seong Chu Lim, Seung Jin Chae, Hyunyong Choi, Young Hee Lee, and Joo-Hiuk Son
Abstract: We present terahertz spectroscopic measurements of Dirac fermion dynamics from a large-scale graphene grown by chemical vapor deposition, on which the carrier density was modulated by electrostatic and chemical doping. The measured frequency-dependent optical sheet conductivity of graphene shows a nontrivial electron density-dependence characteristics, which can be appreciated by a simple Drude model; in a low carrier density regime, the optical sheet conductivity of graphene is constant ( ) regardless of the applied gate voltage, but in a high carrier density regime, it shows a nonlinear behavior ( ; N is the total charge) with respect to the applied gate voltage. A chemically-driven extrinsic doping using viologen, was found to be an efficient method in controlling the equilibrium Fermi level without sacrificing unique carrier dynamics of graphene.