Abstract
We investigate the topological edge modes of surface plasmon polaritons (SPPs) in a non-Hermitian system composed of graphene pair arrays with alternating gain and loss. The topological edge modes emerge when two topologically distinct graphene arrays are connected. The gain and loss present in the system provide additional ways to control the propagation loss and field distributions of the topological edge modes. Moreover, the existence of the topological edge modes is related to the broken parity-time (PT) symmetry. We show the beam diffraction can be steered by tuning the chemical potential of graphene. Thanks to the strong confinement of SPPs, the topological edge modes can be squeezed into a lateral width of ~λ/70. We also show such modes can be realized in lossy graphene waveguides without gain. The study provides a promising approach to realizing robust light transport and optical switches on a deep-subwavelength scale.
Highlights
Metallic waveguides can support surface plasmon polaritons (SPPs) and have sparked enormous interest in manipulating light to circumvent the diffraction limit and may find application in compact devices and nanoscale resolution imaging [1,2,3,4,5]
Topological photonics characterize the collective behavior of the wave functions on the band, providing new and robust way to control the light flows [7]
A topological edge mode emerges at the interface between topological trivial and non-trivial structures characterized by an integer-valued quantity [8]
Summary
Metallic waveguides can support surface plasmon polaritons (SPPs) and have sparked enormous interest in manipulating light to circumvent the diffraction limit and may find application in compact devices and nanoscale resolution imaging [1,2,3,4,5]. According to the ratio between intra- and inter-layer couplings, the winding number is either zero or unity separated by the Dirac point, the spectral degeneracies in Hermitian systems [10] Such modes remain stable against disorders as the structure topology is hard to destroy [7]. One has shown that periodically patterned graphene can have large topological bandgaps and sustains remarkably stable topological edge modes [40]. These properties enable graphene a promising platform to investigate the topological properties of SPPs. The remainder of this work is organized as follows.
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