INTEGER QUANTUM HALL-EFFECT IN DOUBLE-LAYER SYSTEMS

We consider the localization of independent electron orbitals in doubl e-layer two-dimensional electron systems in the strong magnetic-field limit. Our study is based on numerical Thouless number calculations fo r realistic microscopic models, and on transfer-matrix calculations fo r phenomenological network models. The microscopic calculations indica te a crossover regime for weak interlayer tunneling in which the corre lation-length exponent appears to increase. Comparison of network mode l calculations with microscopic calculations casts doubt on their gene ric applicability.