Observation of a Magnetically Induced Wigner Solid

The existence of the magnetic-field-induced liquid-to-solid phase transition in an extreme quantum-limit 2D electron plasma is established for electrons at a high-quality GaAs/GaAlAs heterojunction by detection of a gapless magnetophonon excitation branch with radio-frequency spectroscopy. The phase diagram, determined for Wigner-Seitz to Bohr radius ratio $1.6<\mathrm{}{r}_s<2.5\mathrm{}$, extrapolates to a zero-temperature critical Landau-level filling factor ${\nu }_c=0.23\mathrm{}\pm 0.04$ and a zero-filling-factor melting temperature close to the classical ($r_s\to \infty$) limit.