Collective Dynamics and Defect Generation for Wigner Crystal Ratchets

TL;DR

This study explores how a two-dimensional Wigner crystal interacts with an asymmetric potential under various drives, revealing diverse ratchet behaviors, phase transitions, and conditions for controlling charge flow.

Contribution

It introduces a comprehensive analysis of ratchet effects and phase transitions in Wigner crystals under asymmetric potentials, highlighting new dynamical states and control mechanisms.

Findings

Identification of multiple ratchet regimes including pinned, diode-like, plastic, and elastic ratchets.

Observation of ratchet reversal at high electron filling levels.

Thermal fluctuations can enhance or destroy ratchet effects depending on their strength.

Abstract

We consider a two-dimensional Wigner crystal coupled to a quasi-one-dimensional asymmetric potential under ac or dc driving. As a function of electron density, substrate strength, and ac amplitude, we find that the system exhibits ordered and disordered pinned and dynamical states. Ratchet effects can appear under an applied ac drive and can be associated with pronounced structural changes from a disordered state to a one-dimensional smectic-like state. We observe a pinned phase, a diode-like ratchet where motion only occurs along the easy direction of the substrate asymmetry, a plastic ratchet where motion occurs in both directions but there is only a net drift in the easy direction, and an elastic ratchet where the system forms a crystal without plastic deformation that can still undergo ratcheting. At high filling, we find that there can be a ratchet reversal in which the net drift is along the hard direction of the substrate asymmetry. For weak disorder, there is an Aubry transition to a floating phase where the ratchet effects are lost. We map out the different dynamical phases as a function of substrate strength, filling, ac amplitude, and ac frequency. The ratchet effect on strong substrates is enhanced by thermal fluctuations, but is destroyed when the fluctuations become too large. Based on our results, we suggest new ways to detect Wigner crystals as well as methods for creating new types of devices to control disordered charge flow.