Surface plasmon polaritons are a promising basis for nanoscale photonic devices because they can concentrate light below the diffraction limit and allow for strong light- matter interactions. We demonstrate an efficient nanoscale electrical detector for propagating plasmons, an essential component for integrated plasmonic nanocircuits. Our technique is based on the near-field coupling between guided plasmons and a nanowire field-effect transistor. The intrinsic detection efficiencies of our detectors are approximately 0.1 electrons/plasmon, and the signal can be amplified up to 50 electrons per plasmon using a plasmonic gating effect. Finally, we demonstrate that this near-field circuit can be used to efficiently detect the emission from a single quantum dot that is directly coupled to a plasmonic waveguide.;The second part of this thesis studies phase transitions in nanowires. First, we report observation of a current-driven metal-insulator phase oscillation in two-terminal devices incorporating individual WxV 1-xO2 nanobeams. The frequency of the phase oscillation reaches above 5 MHz for ∼1-mum-long devices. The M-I phase oscillation occurs through the axial drift of a single M-I domain wall driven by Joule heating and the Peltier effect. Second, we characterize the stability of the superconducting dissipationless and resistive states in single-crystalline NbSe2 nanoribbons by transport measurements. Current-driven electrical measurements show voltage steps, indicating the nucleation of phase-slip structures. Well below the critical temperature, the position of the voltage steps exhibits a sharp, periodic dependence as a function of magnetic field. We discuss this phenomenon in the context of two possible mechanisms: the interference of the order parameter and the periodic rearrangement of the vortex lattice within the nanoribbon.;Taken together, these results show that single emitters and single domains can be detected electrically. They are a step towards understanding and controlling nanoscale physical processes at the fundamental component level.
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