I will present results from microwave spectroscopy on two dimensional  electron systems in the 2D electron solid phases that terminate the  fractional quantum Hall liquid series at high magnetic fields [1].  The conductivity spectrum exhibits a resonance, interpreted as the  pinning mode of the electron solid oscillating collectively in the  disorder potential [1,2]. Above a characteristic high temperature,  the resonance disappears due to melting. The melting temperature is  found to be determined ONLY by the many-body interaction between  electrons, given by the Landau level (LL) filling factor. At any  fixed LL filling factor, the melting temperature is insensitive to  the density of 2D electrons. In contrast, the melting temperature for  ANY classical solid is solely determined by its density [3].
References:
[1] Y. P. Chen et al., Phys. Rev. Lett. 93, 206805 (2004).
[2] Y. Chen et al.,  Phys. Rev. Lett. 91, 016801 (2003); R. M. Lewis et al., Phys. Rev. Lett. 93, 176808  (2004); Phys. Rev. B 71, 081301 (2005).
[3] Y. P. Chen et al., Nature Physics 2, 452 (2006).