Abstract-Effects of environmental conditions on the ultrafast carrier dynamics in graphene revealed by terahertz spectroscopy

H. A. Hafez, X. Chai, Y. Sekine, M. Takamura, K. Oguri, I. Al-Naib, M. M. Dignam, H. Hibino, and T. Ozaki

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.165428

A thorough understanding of the stability of graphene under ambient environmental conditions is essential for future graphene-based applications. In this paper, we study the effects of ambient temperature on the properties of monolayer graphene using terahertz time-domain spectroscopy as well as time-resolved terahertz spectroscopy enabled by an optical-pump/terahertz-probe technique. The observations show that graphene is extremely sensitive to the ambient environmental conditions and behaves differently depending on the sample preparation technique and the initial Fermi level. The analysis of the spectroscopic data is supported by van der Pauw and Hall effect measurements of the carrier mobility and carrier density at temperatures comparable to those tested in our THz spectroscopic experiments.

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Abstract-Nonlinear transmission of an intense terahertz field through monolayer graphene

H. A. Hafez¹, I. Al-Naib², K. Oguri³, Y. Sekine³, M. M. Dignam², A. Ibrahim¹,D. G. Cooke⁴, S. Tanaka⁵, F. Komori⁶, H. Hibino³ and T. Ozaki^1,a)

http://scitation.aip.org/content/aip/journal/adva/4/11/10.1063/1.4902096
1 INRS-EMT, Advanced Laser Light Source, INRS, Varennes, Québec J3X 1S2, Canada
2 Department of Physics, Engineering Physics and Astronomy, Queen’s University, Kingston, Ontario K7L 3N6, Canada
3 NTT Basic Research Laboratories, NTT Corporation, Atsugi, Kanagawa 243-0198, Japan
4 Department of Physics, McGill University, Montréal, Québec, H3A 2T8, Canada
5 Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka 819-0395, Japan
6 Institute for Solid State Physics, University of Tokyo, Chiba, 277-8581, Japan
a) Author to whom correspondence should be addressed. Electronic mail: ozaki@emt.inrs.ca
AIP Advances 4, 117118 (2014); http://dx.doi.org/10.1063/1.4902096

We report nonlinear terahertz (THz) effects in monolayer graphene, giving rise to transmission enhancement of a single-cycle THz pulse when the incident THz peak electric field is increased. This transmission enhancement is attributed to reduced photoconductivity, due to saturation effects in the field-induced current and increased intraband scattering rates arising from transient heating of electrons. We have developed a tight-binding model of the response using the length gauge interaction Hamiltonian that provides good qualitative agreement. The model fully accounts for the nonlinear response arising from the linear dispersion energy spectrum in graphene. The results reveal a strong dependence of the scattering time on the THz field, which is at the heart of the observed nonlinear response.