Abstract-Composition control of plasmon-phonon interaction using topological quantum-phase transition in photoexcited (Bi1-xInx)2Se3

Sangwan Sim, Jun Park, nikesh koirala, Seungmin Lee, Matthew J. Brahlek, Jisoo Moon, Maryam Salehi,Jaeseok Kim, Soonyoung Cha, Ji Ho Sung, Moon-Ho Jo, Seongshik Oh, and Hyunyong Choi

ACS Photonics, Just Accepted Manuscript

DOI: 10.1021/acsphotonics.6b00021

Publication Date (Web): May 24, 2016

Copyright © 2016 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.6b00021?journalCode=apchd5

Plasmonics is a technology aiming at light modulation via collective charge oscillations. Topological insulators, where Dirac-like metallic surfaces coexist with normal insulating bulk, have recently attracted great attentions in plasmonics due to their topology-originated outstanding properties. Here, we introduce a new methodology for controlling the interaction of plasmon with phonon in topological insulators, which is a key for utilizing the unique spectral profiles for photonic applications. By using both static and ultrafast terahertz spectroscopy, we show that the interaction can be tuned by controlling the chemical composition of (Bi1-xInx)2Se3micro-ribbon arrays. The topological quantum-phase transition induced by varying the composition drives a dramatic change in the strength of the plasmon-phonon interaction. This was possible due to the availability of manipulating the spatial overlap between topological surface plasmonic states and underlying bulk phonon. Especially, we control the laser-induced ultrafast evolution of the transient spectral peaks arising from the plasmon-phonon interaction by varying the spatial overlap across the topological phase transition. This study may provide a new platform for realizing topological insulator-based ultrafast plasmonic devices.

Abstract-Unconventional Terahertz Carrier Relaxation in Graphene Oxide: Observation of Enhanced Auger Recombination due to Defect Saturation

Jaeseok Kim , Juyeong Oh , Chihun In , Yun-Shik Lee , Theodore B. Norris , Seong Chan Jun , and Hyunyong Choi

http://pubs.acs.org/doi/abs/10.1021/nn406066f

ACS Nano, Just Accepted Manuscript

DOI: 10.1021/nn406066f

Publication Date (Web): February 4, 2014

Copyright © 2014 American Chemical Society

Photoexcited carrier relaxation is a recurring topic in understanding the transient conductivity dynamics of graphene-based devices. For atomically-thin graphene oxide (GO), a simple free-carrier Drude response is expected to govern the terahertz (THz) conductivity dynamics ―same dynamics observed in conventional CVD-grown graphene. However, to date no experimental testimony has been provided on the origin of photo-induced conductivity increase in GO. Here, using ultrafast terahertz (THz) spectroscopy, we show that the photoexcited carrier relaxation in GO exhibits a peculiar non-Drude behavior. Unlike graphene, the THz dynamics of GO show percolation behaviors: as the annealing temperature increases, transient THz conductivity rapidly increases and the associated carrier relaxation changes from mono- to bi-exponential decay. After saturating the recombination decay through defect trapping, a new ultrafast decay channel characterized by multi-particle Auger scattering is observed whose threshold pump fluence is found to be 50 µJ/cm2. The increased conductivity is rapidly suppressed within 1 ps due to the Auger recombination, and non-Drude THz absorptions are subsequently emerged as a result of the defect-trapped high-frequency oscillators.