Evidence for correlated defects in an ultra-clean Wigner crystal in the extreme quantum limit

Low-disorder two-dimensional electron systems in the presence of a strong, perpendicular magnetic field terminate at very small Landau level filling factors in a Wigner crystal (WC), where the electrons form an ordered array to minimize the Coulomb repulsion. The nature of this exotic, many-body, quantum phase is yet to be fully understood and experimentally revealed. Here we probe one of WC’s most fundamental macroscopic parameters, namely the energy gap that determines its low-temperature conductivity, in record-mobility, ultra-high-quality, two-dimensional electrons confined to GaAs quantum wells. The WC domains in these samples contain ≃ 1000 electrons. The measured gaps are a factor of three larger than previously reported for lower quality samples [1,2], and agree remarkably well with values predicted for the lowest-energy, intrinsic, hyper-corelated bubble defects in a WC made of flux-electron composite fermions, rather than bare electrons [3]. The agreement is particularly noteworthy, given that the calculations are done for disorder-free composite fermion WCs, and there are no adjustable parameters. The results attest to the exceptionally high quality of the samples and provide evidence for composite fermion WCs indeed being more stable compared to their electron counterparts.

References:

[1] H. W. Jiang et al., Phys. Rev. B 44, 8107216 (1991).

[2] R. L. Willett et al., Phys. Rev. B 38, 7881 (1988).

[3] A. C. Archer et al., Phys. Rev. B 90, 201309 (2014).