Magneto-Optical Evidence for Fractional Quantum Hall States Down to Filling Factor 1/9 and for Wigner Crystallization
Discontinuities have been observed in the energy dependence on magnetic field of the luminescence line corresponding to two-dimensional (2D) electron-hole recombination in GaAs-AlGaAs heterojunctions at filling factors v = 2/3, 1/3, 4/5, 3/5, 2/5, 1/5, 1/7 and 1/9. We associate these energy position shifts with discontinuous behaviour of the chemical potential due to condensation of the 2D electrons into an incompressible Fermi liquid state and thereby evaluate the energy gaps at fractional filling factors down to 1/9. Below a critical filling factor (v cr = 0.28) and a critical temperature (Tcr =1.4K at 26T) an additional line has been observed in the spectrum which grows in intensity with decreasing v and dominates the luminescence spectrum at v<1/11. Its appearance is accompanied by a strong reduction in integrated intensity, while its relative intensity decreases sharply at v = 1/5, 1/7 and 1/9. The lack of correlation between v cr and the disorder related properties of the system indicates the intrinsic nature of the line which we propose signals the formation of a pinned Wigner solid.
KeywordsMagnetic Field Luminescence Spectrum Filling Factor Spectral Position Luminescence Line
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