title: Terahertz-field-induced nonlinear electron delocalization in Au nanostructures.
abstract: Improved control over the electromagnetic properties of metal nanostructures is indispensable for the development of next-generation integrated nanocircuits and plasmonic devices. The use of terahertz (THz)-field-induced nonlinearity is a promising approach to controlling local electromagnetic properties. Here, we demonstrate how intense THz electric fields can be used to modulate electron delocalization in percolated gold (Au) nanostructures on a picosecond time scale. We prepared both isolated and percolated Au nanostructures deposited on high resistivity Si(100) substrates. With increasing the applied THz electric fields, large opacity in the THz transmission spectra takes place in the percolated nanostructures; the maximum THz-field-induced transmittance difference, 50% more, is reached just above the percolation threshold thickness. Fitting the experimental data to a Drude-Smith model, we found furthermore that the localization parameter and the damping constant strongly depend on the applied THz-field strength. These results show that ultrafast nonlinear electron delocalization proceeds via strong electric field of THz pulses; the intense THz electric field modulates the backscattering rate of localized electrons and induces electron tunneling between Au nanostructures across the narrow insulating bridges without any material breakdown.
authors.affiliation: Department of Physics, Graduate School of Engineering, Yokohama National University , Yokohama 240-8501, Japan.
authors.forename: Katsumasa
authors.initials: K
authors.lastname: Yoshioka
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Minami
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Shudo
authors.forename: Thang D
authors.initials: TD
authors.lastname: Dao
authors.forename: Tadaaki
authors.initials: T
authors.lastname: Nagao
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kitajima
authors.forename: Jun
authors.initials: J
authors.lastname: Takeda
authors.forename: Ikufumi
authors.initials: I
authors.lastname: Katayama
keywords: Terahertz; electron delocalization; metal nanostructures; nonlinear spectroscopy; percolation; quantum tunneling