By making use of circularly polarized light and electrostatic gating, monolayer molybdenum disulfide (${\mathrm{ML}-\mathrm{MoS}}_2$) can form a platform supporting multiple types of charge carriers. They can be discriminated by their spin, valley index, or whether they are electrons or holes. We investigate the collective properties of those charge carriers and are able to identify distinct plasmon modes. We analyze the corresponding dispersion relation, lifetime, and oscillator strength, and calculate the phase relation between the oscillations in the different components of the plasmon modes. All platforms in ML-${\mathrm{MoS}}_2$ support a long-wavelength $\sqrt{q}$ plasmon branch at zero kelvins. In addition to this, for an $n$-component system, $n-1$ distinct plasmon modes appear as acoustic modes with linear dispersion in the long-wavelength limit. These modes correspond to out-of-phase oscillations in the different fermion liquids and have, although being damped, a relatively long lifetime. Additionally, we also find distinct modes at large wave vectors that are more strongly damped by intraband processes.

• Received 24 May 2017
• Revised 18 July 2017

DOI:https://doi.org/10.1103/PhysRevB.96.085405