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The device applications of plasmonic systems such as graphene and two dimensional electron gases (2DEGs) in III-V
heterostructures include terahertz detectors, mixers, oscillators and modulators. These two dimensional (2D) plasmonic
systems are not only well-suited for device integration, but also enable the broad tunability of underdamped plasma
excitations via an applied electric field. We present demonstrations of the coherent coupling of multiple voltage tuned
GaAs/AlGaAs 2D plasmonic resonators under terahertz irradiation. By utilizing a plasmonic homodyne mixing
mechanism to downconvert the near field of plasma waves to a DC signal, we directly detect the spectrum of coupled
plasmonic micro-resonator structures at cryogenic temperatures. The 2DEG in the studied devices can be interpreted as
a plasmonic waveguide where multiple gate terminals control the 2DEG kinetic inductance. When the gate tuning of the
2DEG is spatially periodic, a one-dimensional finite plasmonic crystal forms. This results in a subwavelength structure,
much like a metamaterial element, that nonetheless Bragg scatters plasma waves from a repeated crystal unit cell. A
50% in situ tuning of the plasmonic crystal band edges is observed. By introducing gate-controlled defects or simply
terminating the lattice, localized states arise in the plasmonic crystal. Inherent asymmetries at the finite crystal
boundaries produce an induced transparency-like phenomenon due to the coupling of defect modes and crystal surface
states known as Tamm states. The demonstrated active control of coupled plasmonic resonators opens previously
unexplored avenues for sensitive direct and heterodyne THz detection, planar metamaterials, and slow-light devices.
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