Ultra-long wavelength Dirac plasmons in graphene capacitors

TL;DR

This paper demonstrates ultra-long-wavelength Dirac plasmons in graphene capacitors at GHz frequencies, revealing low-loss plasmonic resonances that enable precise electronic property measurements and potential applications in microwave detection and tunable superlattices.

Contribution

It introduces a plasma resonance capacitor using hBN-encapsulated graphene at cryogenic temperatures, achieving GHz plasmons with high quality factors and enabling detailed study of Dirac plasmonics in the low-frequency regime.

Findings

Demonstrated 40 GHz plasmon resonance in graphene capacitor

Achieved a quality factor of approximately 2

Enabled precise measurement of electronic compressibility

Abstract

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