Abstract-Extremely confined terahertz surface plasmon-polaritons in graphene-metal structures

Xuefeng Gu, I-Tan Lin, and Jia-Ming Liu

Department of Electrical Engineering, University of California Los Angeles, Los Angeles, California 90095, USA 

http://apl.aip.org/resource/1/applab/v103/i7/p071103_s1?isAuthorized=no

A deep subwavelength terahertz plasmonic waveguide based on graphene-metal hybrid structure is proposed. A broadband mode confinement down to 1/100 of the free-space wavelength λ₀ with a loss of 0.6 dB/λ₀ can be achieved when the intra-band electron relaxation time is 100 ps. We show that very narrow slits with an appropriate periodicity created in the metal layer can serve as a grating to efficiently excite the surface plasmon-polariton mode with a normally incident terahertz beam, which can be further exploited for investigation of both interesting physics and innovative applications.

Terahertz optical properties of multilayer graphene: Experimental observation of strong dependence on stacking arrangements and misorientation angles

http://prb.aps.org/abstract/PRB/v86/i23/e235446

I-Tan Lin¹, Jia-Ming Liu^1,*, Kai-Yao Shi², Pei-Shan Tseng², Kuang-Hsiung Wu², Chih-Wei Luo², and Lain-Jong Li^3
1Electrical Engineering Department, University of California, Los Angeles, Los Angeles, California 90095, USA
²Department of Electrophysics, National Chiao-Tung University, Hsinchu, Taiwan
³Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan

Received 8 November 2012; published 27 December 2012

The optical conductivity of monolayer and multilayer graphene in the terahertz spectral region is experimentally measured using terahertz time-domain spectroscopy. The stacking arrangement and the misorientation angle of each sample are determined by Raman spectroscopy. The chemical potential of each sample is measured using ultrafast midinfrared pump-probe spectroscopy to be 63 or 64 meV for all samples. The intraband scattering rate can be obtained by fitting the measured data with theoretical models. Other physical parameters, including carrier density, dc conductivity, and carrier mobility, of each sample can also be deduced from the theoretical fitting. The fitting results show the existence of misoriented or AA-stacked layers with an interaction energy of α₁=217 meV in our multilayer samples. Here we show that the scattering rate strongly depends on the stacking arrangement of the sample. High scattering rates and high optical conductivity are associated with AA-stacked samples, while lower ones are associated with misoriented multilayer graphene. This implies that the THz optoelectronic properties of multilayer graphene can be tuned by purposefully misorienting layers or employing different stacking schemes.

©2012 American Physical Society

Abstract-Terahertz optical properties of multilayer graphene: Experimental observation of strong dependence on stacking arrangements and misorientation angles

I-Tan Lin, Jia-Ming Liu, Kai-Yao Shi, Pei-Shan Tseng, Kuang-Hsiung Wu, Chih-Wei Luo, and Lain-Jong Li

The optical conductivity of monolayer and multilayer graphene in the terahertz spectral region is experimentally measured using terahertz time-domain spectroscopy. The stacking arrangement and the misorientation angle of each sample are determined by Raman spectroscopy. The chemical potential of each simple is measured using ultrafast mid-infrared pump-probe spectroscopy to be 63 or 64 meV for all samples. The intraband scattering rate can be obtained by fitting the measured data with theoretical models. Other physical parameters, including carrier density, DC conductivity, and carrier mobility, of each sample can also be deduced from the theoretical fitting. The fitting results show the existence of misoriented or AA-stacked layers with an interaction energy of alpha sub 1 = 217 meVin our multilayer samples. Here we show that the scattering rate strongly depends on the stacking arrangement of the sample. High scattering rates and high optical conductivity are associated with AA-stacked samples, while lower ones are associated with misoriented multilayer graphene. This implies that the THz optoelectronic properties of multilayer graphene can be tuned by purposefully misorienting layers or employing different stacking schemes.