Directional dependence of the plasmonic gain and nonreciprocity in drift-current biased graphene

TL;DR

This paper explores how drift-current biased graphene exhibits nonreciprocal surface plasmon propagation and amplification, with models showing significant directional effects and potential for unidirectional plasmonic devices.

Contribution

It compares Galilean and relativistic Doppler shift models to predict nonreciprocal plasmon behavior and demonstrates regimes of plasmon amplification in biased graphene.

Findings

Galilean model predicts stronger spectral asymmetries.

Both models show regimes of nonreciprocal plasmon amplification.

Amplification rates are higher in the relativistic Doppler shift model.

Abstract

Here, we investigate the nonreciprocal propagation and amplification of surface plasmons in drift-current biased graphene, using both Galilean and relativistic-type Doppler shift transformations of the graphene's conductivity. Consistent with previous studies, both conductivity models predict strongly nonreciprocal propagation of surface plasmons due to the drag effect caused by the drifting electrons. In particular, the Galilean Doppler shift model leads to stronger spectral asymmetries in the plasmon dispersion with regimes of unidirectional propagation. Remarkably, it is shown that both conductivity models predict regimes of nonreciprocal plasmon amplification in a wide angular sector of in-plane directions when the drift-current biased graphene sheet is coupled to a plasmonic substrate (namely, SiC), with the plasmon amplification rate being substantially higher for the relativistic Doppler shift model.