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

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.