Electronics-Regime Plasmonics in Reduced Dimensions

Plasma is the state of matter that comprises all the stars in our universe, and even occupies the vast space in between stars and in between galaxies, making up over 99 percent of ordinary matter. Yet under the conditions present here on Earth we find that the free electrons within solid-state metals and semiconductors provide a more tractable type of system in which to study certain plasma behaviors. These behaviors include volume oscillations of electrons, or bulk plasmons, as well as propagating electron density waves on the conductor surface, known as surface plasmons. Surface plasmons typically occur in the optical regime, and the term "plasmonics" generally refers to the field that is based on manipulation of surface plasmons in optics.;This thesis, however, focuses on measurements and applications of plasmons in the GHz frequency range, the electronics regime. Surface plasmons have not been observed at GHz, but when electrons are perfectly confined into two dimensions, as in a GaAs/AlGaAs two-dimensional electron gas (2DEG), the physics changes such that these two-dimensional (2D) plasmons are observable at frequencies as low as a few GHz. This thesis presents various devices based upon GHz 2D plasmons in order to demonstrate how 2D plasmons can contribute to electronics. Like surface plasmons, 2D plasmons can exhibit small wavelengths relative to electromagnetic waves, but to a much greater degree, resulting in the ability to create dramatically miniaturized analogs to the passive electromagnetic devices that are ubiquitous in analog electronics.;We can further reduce the electron system to consider one-dimensional plasmons. One-dimensional systems such as carbon nanotubes, and GaAs/AlGaAs quantum wires, studied in this thesis, exhibit quantization of electron channels. When the gate bias of a quantum wire is gradually increased, the conductance of the wire increases by discrete steps of 2e² /h, the conductance quantum, as observed in many DC measurements. Here we increase the measurement frequency into the GHz range, and attempt to observe plasmons propagating in these 1D channels, with possible quantization-related features in the wire's high-frequency properties. Such measurements have the potential to improve our understanding of the fundamental physics of 1D systems.