Acoustic study of Wigner crystal melting in n-GaAs/AlGaAs at high magnetic fields

We have measured absorption and velocity of surface acoustic waves (SAWs) in high-mobility samples n-GaAs/AlGaAs in magnetic fields (12–18) T (filling factors ν = 0.18–0.125) at temperatures T = (40–340) K and SAW frequencies f = (30–300) MHz. From the measurement data, the complex AC conductance, σ^AC(ω) ≡ σ₁(ω)—iσ₂(ω) and its dependences on frequency, temperature, and the amplitude of the SAW-induced electric field were found. We conclude that in the studied interval of the magnetic field and at T < 200 mK, the electronic systems forms pinned Wigner crystal, the so-called Wigner glass. The estimate of the correlation (Larkin) length of the Wigner glass is about 3 μm, which is much larger than both the distance between the electrons and the magnetic length in the studied field range. At some temperature T_m, the temperature dependences of both components of the complex conductance get substantially changed: from the dielectric behavior at T < T_m to the metallic one at T > T_m. We ascribed this change of the conduction mechanism to melting of the Wigner crystal and studied the dependence of the so-defined melting temperature on the electron filling factor. [This work was supported by RFBR 14-02-00232, NSF Cooperative Agreement DMR-1157490, the State of Florida, the Gordon and Betty Moore Foundation through the EPiQS initiative Grant GBMF4420, and the NSF MRSEC Grant DMR-1420541.]