Ultra-long wavelength Dirac plasmons in graphene capacitors

Abstract

Graphene is a valuable 2D platform for plasmonics as illustrated in recent\nTHz and mid-infrared optics experiments. These high-energy plasmons however,\ncouple to the dielectric surface modes giving rise to hybrid plasmon-polariton\nexcitations. Ultra-long-wavelengthes address the low energy end of the plasmon\nspectrum, in the GHz-THz electronic domain, where intrinsic graphene Dirac\nplasmons are essentially decoupled from their environment. However experiments\nare elusive due to the damping by ohmic losses at low frequencies. We\ndemonstrate here a plasma resonance capacitor (PRC) using hexagonal\nboron-nitride (hBN) encapsulated graphene at cryogenic temperatures in the near\nballistic regime. We report on a $100\\;\\mathrm{\\mu m}$ quarter-wave plasmon\nmode, at $40\\;\\mathrm{GHz}$, with a quality factor $Q\\simeq2$. The accuracy of\nthe resonant technique yields a precise determination of the electronic\ncompressibility and kinetic inductance, allowing to assess residual deviations\nfrom intrinsic Dirac plasmonics. Our capacitor GHz experiment constitutes a\nfirst step toward the demonstration of plasma resonance transistors for\nmicrowave detection in the sub-THz domain for wireless communications and\nsensing. It also paves the way to the realization of doping modulated\nsuperlattices where plasmon propagation is controlled by Klein tunneling.\n