▎ 摘　　要

In analogy to Tamm states in electronic systems, plasmonic Tamm states at the edge of terminated graphene plasmonic crystals are proposed. In contrast to plasmonic Tamm states that exist at the interface between metal-insulator-metal Bragg reflectors and metals, an edge-matching layer should be adopted to compensate the unique extra reflection phase at graphene terminals. The width of the edge-matching layer is optimized by the generalized Wiener-Hopf method according to the phase-matching condition. Moreover, graphene plasmonic crystals with merely two unit cells can compress electromagnetic fields into an extremely small mode volume with remarkable intensity enhancement by virtue of the graphene plasmonic Tamm states. Specifically, both the electric field and magnetic field intensities can be enhanced by 80 times in the ultracompact device with the length of 108.2 nm, which is more than 90 times shorter than the operation wavelength of 10 mu m. The robust confinement mechanism of plasmonic Tamm states enables propagating plasmons trapping and enhancing the electromagnetic field in a planar landscape. Our results open an avenue for developing deep-subwavelength integrated graphene-based trappers, resonators, and biosensors and pave the way for ultracompact on-chip applications.