[PhD Thesis Presentation] - Jui-Yin Lin - Transport properties of strongly correlated 2D electrons confined in microchannels

Abstract:

Wigner crystal is the solid phase of strongly correlated electrons. The main theme of this thesis work is employing a two-dimensional Wigner solid (WS) formed on the surface of liquid helium to probe interplay between, on the one hand, strong internal forces arising from electron-electron interaction and, on the other hand, external forces due to substrate and applied electrostatic potentials. To accomplish these studies we developed and employed a number of microchannel devices to confine WS system and measure its transport properties. First, we characterize the transport properties of a homogeneous electron crystal, an island of WS, and an inhomogeneous electron crystal in a microchannel geometry. We show how interplay between transport regimes of two individual electron crystals effect the overall I-V curves. A further study of WS system of varied size demonstrates how the energy dissipates from the edges of electron crystal through emission of ripplons, which thus affects the breaking of the strong coupling of WS with substrate excitations. Then, by introducing an external spatial periodic potential, we observed suppression of WS-ripplon coupling and re-entrant melting of WS when the amplitude of external potential is sufficiently high. We interpret these phenomena as arising from the structural phase transitions in WS confined in a microchannel with spatially varied potential. This work is also relevant to the general study of the Frenkel-Kontorova model of interacting particles subject to a periodic substrate potential. Finally, some interesting features in the transport of strongly-correlated electrons have been studied in a T-shaped microchannel geometry. In particular, experiments showed a breakdown of the conventional Drude bahaviour at sufficiently low temperatures and high electron densities, which could be due to effect of inertia of the surface excitations coupled to the WS.