We investigate the transport properties of a ladder with two random dimer (RD) chains.It is found that there are two extended states in the ladder with identical RD chains and a critical state regarded as an extended state in the ladder with pairing RD chains.Such a critical state is caused by the chiral symmetry.The ladder with identical RD chains can be decoupled into two isolated RD chains and the ladder with pairing RD chains can not.The analytic expressions of the extended states are presented for the ladder with identical RD chains.
We investigate the transport properties of a random binary side-coupled chain by using the transfer-matrix technique. It is found that there are resonant states in the systems with short-range correlations between the host chain atoms and the side-coupled atoms. The analytic expressions for the extended states are also presented in the systems with the side couplings between like atoms and between unlike atoms.
