Correlation‐induced phase transitions in two‐dimensional electron systems

The electrons in inversion or accumulation layers of MOSFETS or in semiconductor‐semiconductor interfaces show prominent many‐body effects. A new theory of the correlation energy is developed for these electrons such that the results are applicable to a wide density range. The ground‐state energy is obtained for all densities. It is continuous and convergent, but changes its analytical form at r s = 1.414. Associated with this change is a divergence of the compressibility that occurs at r s = 1.989. Hence, around this r s , the system can be considered to be in a liquidlike state. In the [001] direction of silicon inversion layers, the two valleys, occupied equally by the electrons at high densities, may be populated unevenly due to electron correlations. This unbalance will cause a valley occupancy phase transition at r s = 8.011, in close agreement with a recent experiment. Under a magnetic field, the susceptibility is enhanced nonlinearly when the density of electrons is reduced. This enhancement becomes very strong toward r s = 13.0, beyond which a spin‐polarized state is favored.