Low-loss forward and backward surface plasmons in a semiconductor nanowire coated by helical graphene strips

TL;DR

This paper introduces a theoretical model for low-loss surface plasmons on a semiconductor nanowire coated with helical graphene strips, revealing tunable forward and backward wave propagation with potential applications in nanophotonics.

Contribution

It derives explicit dispersion equations for hybrid surface plasmons on a graphene-coated nanowire with helical strips, identifying low-loss spoof plasmons with tunable properties.

Findings

Spoof plasmons are low-loss and tunable.

Dispersion equations for hybrid plasmons are explicitly derived.

Surface wave properties can be controlled by geometric parameters.

Abstract

In the long-wavelength approximation, the effective conductivity tensor is introduced for graphene ribbons (strips) placed periodically at the interface between two media. The resulting conducting surface is considered as a coating for semiconductor nanowire. For the hybrid waves of such nanowire the dispersion equations are obtained in explicit form. Two types of surface plasmons are found to exist: (i) the modified surface plasmons, which originate from the ordinary surface plasmons of a graphene-coated semiconductor nanowire, and (ii) the spoof plasmons, which arise on the array of graphene ribbons and may possess forward-wave and backward-wave dispersion. It is revealed that the spoof surface plasmons are low-loss ones, and their frequencies, field-confinement and group velocities can be tuned widely by adjusting the coil angle and width of helical graphene strips.