Wigner Solid. II. Transport Properties

Abstract

The surface of superfluid helium supporting the 2D Wigner solid does not impose an impurity potential or a regular potential on the electron lattice. At a finite frequency of the driving electric field, this solid is a quite mobile object. Hence, the system of SEs on liquid helium provides us with a unique possibility for studying transport properties of the extremely correlated state of interface electrons. As discussed in the last chapter, under typical conditions, the electron crystal is strongly coupled to surface dimples. It is obvious that the conductivity of the WS depends crucially on the frequency of the signal ω. If ω < ω ₁, the surface dimples of liquid ⁴He are involved in motion of the electron lattice, which increases the effective mass and affects the effective collision frequency of electrons. Soon after the observation of the coupled phonon—ripplon modes reported by Grimes and Adams, mobility anomalies at the WS transition point were reported in [101, 232]. An interesting mobility minimum near the melting temperature of the 2D electron solid supported by the liquid helium surface was reported in [50, 233]. We have already seen this anomaly in Fig. 3.1 as a maximum of the inverse quantity 1/µ vs. temperature. The narrow excess scattering observed was reportedly identical to the temperature-dependent losses associated with the superfluid transition in thin helium films However, there was no conclusive proof that this peak is caused by dissociation of dislocation pairs due to the Kosterlitz—Thouless melting mechanism.