Moving crystal phases of a quantum Wigner solid in an ultra-high-quality 2D electron system

In low-disorder, two-dimensional electron systems (2DESs), the fractional quantum Hall states at very small Landau level fillings (ν) terminate in a Wigner solid (WS) phase, where electrons arrange themselves in a periodic array. The WS is typically pinned by the residual disorder sites and manifests an insulating behavior, with non-linear current-voltage (I-V) and noise characteristics [1,2]. We report here measurements on an ultra-low-disorder, dilute 2DES, confined to a GaAs quantum well. In the insulating phases, we observe remarkable non-linear I-V and noise characteristics as a function of increasing current, with current thresholds delineating three distinct phases of the WS: a pinned phase (P1) with very small noise, a second phase (P2) in which dV /dI fluctuates between positive and negative values and is accompanied by very high noise, and a third phase (P3) where dV /dI is nearly constant and small, and noise is about an order of magnitude lower than in P2. In the depinned (P2 and P3) phases, the noise spectrum also reveals well-defined peaks at frequencies that vary linearly with the applied current, suggestive of washboard frequencies. We discuss the data in light of a recent theory that proposes different dynamic phases for a driven WS [3].

References:

1. [1] V. J. Goldman et al., Phys. Rev. Lett. 65, 2189 (1990).
   
   [2] Y. P. Li et al., Phys. Rev. Lett. 67, 1630 (1991).
   
   [3] C. Reichhardt et al., J. Phys.: Condens. Matter 35, 325603 (2023).