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Paper IPM / Physic / 6810  


Abstract:  
We present a variational study of both unpaired and spinsinglet paired states induced in a twodimensional electron gas at low density by a perpendicular magnetic field. It is based on an improved circularcell approximation which leads to a number of closed analytical results. The groundstate energy of the Wigner crystal containing a single electron per cell in the lowest Landau level is obtained as a function of the filling factor ν: the results are in good agreement with those of earlier approaches and predict ν_{c} ≈ 0.25 for the upper filling factor at which the solidliquid transition occurs. A novel localized state of spinsinglet electron pairs is examined and found to be a competitor of the unpaired state for filling factor ν > 1. The corresponding phase boundary is quantitatively displayed in the magnetic fieldelectron density plane.
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