Abstract-Terahertz imaging and spectroscopy of large-area single-layer graphene

J. L. Tomaino, A. D. Jameson, J. W. Kevek, M. J. Paul, A. M. van der Zande, R. A. Barton, P. L. McEuen, E. D. Minot, and Yun-Shik Lee

https://www.osapublishing.org/abstract.cfm?rwjcode=oe&uri=oe-19-1-141

We demonstrate terahertz (THz) imaging and spectroscopy of a 15 × 15-mm2single-layer graphene film on Si using broadband THz pulses. The THz images clearly map out the THz carrier dynamics of the graphene-on-Si sample, allowing us to measure sheet conductivity with sub-mm resolution without fabricating electrodes. The THz carrier dynamics are dominated by intraband transitions and the THz-induced electron motion is characterized by a flat spectral response. A theoretical analysis based on the Fresnel coefficients for a metallic thin film shows that the local sheet conductivity varies across the sample from σs = 1.7 × 10−3 to 2.4 × 10−3 Ω−1 (sheet resistance, ρs = 420 - 590 Ω/sq).

© 2011 OSA

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Abstract-Terahertz-triggered phase transition and hysteresis narrowing in a nanoantenna patterned vanadium dioxide film

ZACHARY J. THOMPSON, Andrew J. Stickel, YOUNG-GYUN JEONG, SANGHOON HAN, BYUNG HEE SON, MICHAEL J. PAUL, BYOUNGHWAK LEE, ALI MOUSAVIAN, GIWAN SEO, Hyun-Tak Kim, Yun-Shik Lee, and Dai-Sik Kim

Nano Lett., Just Accepted Manuscript

DOI: 10.1021/acs.nanolett.5b01970

Publication Date (Web): August 24, 2015

Copyright © 2015 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.5b01970

We demonstrate that high-field THz pulses trigger transient insulator-to-metal transition in a nanoantenna patterned vanadium dioxide thin film. THz transmission of vanadium dioxide instantaneously decreases in the presence of strong THz fields. The transient THz absorption indicates that strong THz fields induce electronic insulator-to-metal transition without causing a structural transformation. The transient phase transition is activated on the sub-cycle time scale during which the THz pulse drives the electron distribution of vanadium dioxide far from equilibrium and disturb the electron correlation. The strong THz fields lower the activation energy in the insulating phase. The THz-triggered insulator-to-metal transition gives rise to hysteresis loop narrowing, while lowering the transition temperature both for heating and cooling sequences. THz nanoantennas enhance the field-induced phase transition by intensifying the field strength and improve the detection sensitivity via antenna resonance. The experimental results demonstrate a potential that plasmonic nanostructures incorporating vanadium dioxide can be the basis for ultrafast, energy-efficient electronic and photonic 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.

High-field terahertz response of graphene

M J Paul¹, Y C Chang², Z J Thompson¹, A Stickel¹, J Wardini¹, H Choi³, E D Minot¹, T B Norris^2,4 and Yun-Shik Lee¹

tnorris@umich.edu                            
¹ Department of Physics, Oregon State University, Corvallis, OR 97331, USA
² Center for Ultrafast Optical Science and Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109, USA
³ School of Electrical and Electronic Engineering, Yonsei University, Seoul, Republic of Kore
a

http://m.iopscience.iop.org/1367-2630/15/8/085019
We investigate the response of multi-layer epitaxial graphene and chemical vapor deposition (CVD)-grown single-layer graphene to strong terahertz (THz) fields. Contrary to theoretical predictions of strong nonlinear response, the transmitted fields exhibit no harmonic generation, indicating that the nonlinear response is limited by fast electron thermalization due to carrier–carrier scattering. The fast electron heating gives rise to large THz transmission enhancement (> 15%) in single-layer CVD graphene at high THz fields (E_THz > 10 kV cm⁻¹). The nonlinear effects exhibit non-Drude behavior in the THz conductivity, where THz fields induce extreme non-equilibrium electron distributions

Abstract-Terahertz Excitation of a Coherent Λ-Type Three-Level System of Exciton-Polariton Modes in a Quantum-Well Microcavity

J. L. Tomaino¹, A. D. Jameson¹, Yun-Shik Lee^1,*, G. Khitrova², H. M. Gibbs², A. C. Klettke³, M. Kira³, and S. W. Koch^3 
1Department of Physics, Oregon State University, Corvallis, Oregon 97331, USA
²Optical Sciences Center, University of Arizona, Tucson, Arizona 85721, USA
³Department of Physics and Material Sciences Center, Philipps-University, 35032 Marburg, Germany

http://prl.aps.org/abstract/PRL/v108/i26/e267402

Interactions of few-cycle terahertz pulses with the induced optical polarization in a quantum-well microcavity reveal that the lower and higher exciton-polariton modes together with the optically forbidden 2p-exciton state form a unique Λ-type three-level system. Pronounced nonlinearities are observed via time-resolved strong-terahertz and weak-optical excitation spectroscopy and explained with a fully microscopic theory. The results show that the terahertz pulses strongly couple the exciton-polariton states to the 2p-exciton state while no resonant transition between the two polariton levels is observed.

© 2012 American Physical Society

URL:

http://link.aps.org/doi/10.1103/PhysRevLett.108.267402

DOI:

10.1103/PhysRevLett.108.267402

PACS:

78.67.De, 42.55.Sa, 71.35.Cc, 78.47.jb