Plasmons and the quantum limit in semiconductor wires

We report on the observation by Raman scattering of one-dimensional plasmons in deep-etched wires with lateral sizes w down to 30 nm. We determine the dispersion of these collective excitations down to 45 nm, well beyond the transition to a single one-dimensional subband occupancy $\left(w\sim 60\mathrm{nm}\right),$ and demonstrate that they can be well described both within the random-phase approximation and the Lüttinger liquid theory. In thinner wires, the Raman spectra reduce to a single undispersive low-energy line which we attribute to a plasmon localized by longitudinal disorder in the external potential.