Plasmonic gain in current biased tilted Dirac nodes

TL;DR

This paper demonstrates that current-biased tilted Dirac materials like WTe₂ can exhibit plasmonic gain without external media, enabling highly collimated, amplified surface plasmons through electrical biasing.

Contribution

It introduces a novel mechanism for plasmonic gain in 2D materials using electrical current biasing, eliminating the need for external gain media.

Findings

Prominent plasmonic gain observed at accessible current levels.

Amplified plasmons are highly collimated perpendicular to Dirac node tilt.

The effect is demonstrated in WTe₂ with a tilted Dirac model.

Abstract

Surface plasmons, which allow extreme confinement of light, suffer from high intrinsic electronic losses. It has been shown that stimulated emission of electrons can transfer energy to plasmons and compensate for the high intrinsic losses. To-date, these realizations have relied on introducing an external gain media coupled to the surface plasmon. Here, we propose that plasmons in two-dimensional materials with closely located electron and hole Fermi pockets can experience gain, when an electrical current bias is applied along the displaced electron-hole pockets, without the need for an external gain media. As a prototypical example, we consider WTe$_2$ from the family of 1T$'$-MX$_2$ materials, whose electronic structure can be described within a type-II tilted massive Dirac model. We find that the nonlocal plasmonic response experiences prominent gain for experimentally accessible currents on the order of mA$\mu$m$^{-1}$. Furthermore, the group velocity of the plasmon found from the isofrequency curves imply that the amplified plasmons are highly collimated along a direction perpendicular to the Dirac node tilt when the electrical current is applied along it.