Two-Path Solid-State Interferometry Using Ultra-Subwavelength 2D   Plasmonic Waves
  We report an on-chip solid-state Mach-Zehnder interferometer operating on two-dimensional (2D) plasmonic waves at microwave frequencies. Two plasmonic paths are defined with GaAs/AlGaAs 2D electron gas 80 nm below a metallic gate. The gated 2D plasmonic waves achieve a velocity of ~c/300 (c: free-space light speed). Due to this ultra-subwavelength confinement, the resolution of the 2D plasmonic interferometer is two orders of magnitude higher than that of its electromagnetic counterpart at a given frequency. This GHz proof-of-concept at cryogenic temperatures can be scaled to the THz IR range for room temperature operation, while maintaining the benefits of the ultra-subwavelength confinement. 
Kitty Y. M. Yeung, Hosang Yoon, William Andress, Ken West, Loren   Pfeiffer and Donhee Ham
cond-mat.mes-hall cond-mat.mtrl-sci