Below a critical filling factor (${\nu }_{\mathit{c}}$=0.28) and critical temperature (${\mathit{T}}_{\mathit{c}}$=1.4 K at 26 T) an additional line has been observed in the luminescence spectrum of a GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterojunction; it grows in intensity with decreasing ν, dominating the spectrum at ν<1/11. Its appearance is accompanied by a strong reduction in overall integrated intensity, while its relative intensity decreases sharply at ν=1/5, 1/7, and 1/9. The lack of correlation between ${\nu }_{\mathit{c}}$ 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.

• Received 7 August 1990

DOI:https://doi.org/10.1103/PhysRevLett.66.926