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Niyaz R. Beysengulov - Japon

Electrons on liquid helium : Wigner crystal in confined geometry


The experimental study and theoretical description of the electron systems in reduced dimensionality are one of the milestones in condensed matter physics [1]. The qualitative description of such systems is different from that in 3D due to the enhancement of the interactions in a confined geometry. Interactions become even more important in the limit when the long-rang Coulomb potential predominates over kinetic energy and the electron system is expected to become a periodically ordered solid known as the Wigner crystal.

Here we present an experimental study of Wigner crystallisation of surface state electrons (SSE) formed on liquid helium and confined in a microchannel. Quasi-1D confinement was created by applying voltages to several electrodes : Bottom-Gate (Vbg) and top Split-Gate (Vsg) electrodes. Application of different voltages to these electrodes allows us to precise control of the confinement parameters : the potential depth, which controls the density of the electron system, and the effective width of the channel. The electric current was measured as a function of voltages applied to these electrodes. SSE in the Wigner crystal state form specific bound states with ripplons (surface capillary waves), which effectively increases the mass of electron system. Thus, the transition of the electron system into the ordered state was detected by an appearance of strong nonlinear features in the transport characteristics.

Detailed transport measurements at different temperatures (T = 0.6 – 1.3 K) enable us to build a liquid/solid phase diagram of electron system in a q-1D confinement geometry. The observation of a unique behaviour of interacting systems in confinement - reentrant melting [2] - allows us to identify the number of electron rows formed in the microchannel (from a single chain up to 20 electron rows). The structural phase diagram based on a simple electrostatic model is in good agreement with the experimental observations.

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