Plasmons (1) are collective density oscillations that pertain to charged particles, such as electrons and holes in solids. Although plasmons are often associated with metals, they are being actively explored for graphene and related two-dimensional materials (2DMs). Graphene plasmons (GPs) (2) can achieve active functionalities in diverse device types. For example, mid-infrared (mid-IR) GPs have been used to enhance mid-IR photodetectors (3), vibrational sensing of surface-adsorbed polymers (4), and label-free detection of protein monolayers (5). On page 246 of this issue, Chakraborty et al. (6) show that tunable graphene optical properties and GPs can be used to modulate the emission of a terahertz (THz) quantum cascade laser (7). Electromagnetic waves in the THz range (frequencies ν between 0.3 and 10 THz, or wavelengths γ between 50 µm and 1 mm) can penetrate many materials and have many applications in imaging and spectroscopy.
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