Melting of a 2D quantum electron solid in high magnetic field

The melting temperature T m of a solid is generally determined by its solid–liquid transition on being heated at a fixed pressure, usually ambient pressure. It is also determined indirectly by the density n by means of the equation of state. This remains true even for solid helium 1 , in which quantum effects often lead to unusual properties 2 . Here, we present experimental evidence to show that for a two-dimensional (2D) solid formed by electrons in a semiconductor sample under a strong perpendicular magnetic field 3 ( B ), T m is not controlled by n , but effectively by the quantum correlation between the electrons through the Landau level filling factor ν = n h / e B (where h is the Planck constant and e is the electronic charge). Such melting behaviour, different from that of all other known solids (including a classical 2D electron solid at zero magnetic field 4 ), suggests the quantum nature of the magnetic-field-induced electron solid. Moreover, T m increases with the strength of the sample-dependent disorder that tends to pin the electron solid in place.