Plasmons in tunnel-coupled graphene layers: backward waves with quantum cascade gain

TL;DR

This paper demonstrates that graphene-insulator-graphene tunnel structures can act as plasmonic gain media through stimulated tunneling, leading to backward wave propagation and potential applications in nanoscale photonics.

Contribution

It introduces a novel mechanism for plasmonic gain in graphene heterostructures based on electron tunneling and emission of coherent plasmons, highlighting unique linear band structure effects.

Findings

Resonant tunneling with plasmon emission at specific frequencies.

Negative group velocity in plasmon dispersion due to tunneling.

Potential for plasmonic amplification in graphene-based devices.

Abstract

Plasmons in van der Waals heterostructures comprised of graphene and related layered materials demonstrate deep subwavelength confinement and large propagation length. In this letter, we show that graphene-insulator-graphene tunnel structures can serve as plasmonic gain media. The gain stems from the stimulated electron tunneling accompanied by the emission of coherent plasmons under interlayer population inversion. The probability of tunneling with plasmon emission appears to be resonantly large at certain values of frequency and interlayer voltage corresponding to the transitions between electron states with collinear momenta - a feature unique to the linear band structure of graphene. The dispersion of plasmons undergoes a considerable transformation due to the tunneling as well, demonstrating negative group velocity in several frequency ranges.