THEORIES FOR NU=1 2 IN SINGLE-LAYER AND DOUBLE-LAYER SYSTEMS/

Recent experiments have shown that a quantized Hall plateau can occur in double-layer systems at total filling factor nu = 1/2, though there is no plateau at nu = 1/2 in a normal single-layer system. For the si ngle-layer system, considerable insight has been provided by a theory based on the fermion Chem-Simons picture, where the electrons are tran sformed into fermions that carry two flux quanta of a Chern-Simons gau ge field. A similar picture can be used to characterize ground states which have been proposed for the two-layer system.