Pinning Mode Frequency Tuned by Asymmetric Bias in a GaAs Two Dimensional Electron System in the Wigner Solid Regime*

Electrons in two-dimensional electron systems (2DES) form pinned Wigner crystals at the low Landau filling (ν) termination of the fractional quantum Hall effect (FQHE) series. In clean samples, microwave pinning mode resonances are understood to be indicative of these crystal states. Pinning mode spectroscopy has been used extensively in the study of these solids [1,2]. It has been suggested that disorder arising from interface roughness, due to its small spatial correlation length, contributes the most toward the resonance frequency [3].
We test this theory in a GaAs 2DES by shifting the charge towards the walls of the well with front and back gates. Charge is added to the 2D layer with one of the gates and removed with the second gate so the total density remains unchanged. The amount of charge moved by a single gate is Δn. We find that the resonances at ν from 0.208 to 0.150 are blue shifted by~35% upon an asymmeterization of Δn=0.64×10¹⁰cm^-2.

1 G.Sambandamurthy, et al., Solid State Comm. 140, 100-106 (2006)
2 Y.Chen et al., PRL. 93, 206805 (2004)
3 H.A.Fertig, PRB 59, 2120 (1999)