Integer quantum Hall effect in double-layer systems

We consider the localization of independent electron orbitals in double-layer two-dimensional electron systems in the strong magnetic-field limit. Our study is based on numerical Thouless number calculations for realistic microscopic models, and on transfer-matrix calculations for phenomenological network models. The microscopic calculations indicate a crossover regime for weak interlayer tunneling in which the correlation-length exponent appears to increase. Comparison of network model calculations with microscopic calculations casts doubt on their generic applicability.