Delocalization and conductance quantization in one-dimensional systems

We investigate the delocalization and conductance quantization in finite onedimensional chains with only off-diagonal disorder coupled to leads. It is shown that the appearence of delocalized states at the middle of the band under correlated disorder is strongly dependent upon the even-odd parity of the number of sites in the system. In samples with inversion symmetry the conductance equals 2e/h for odd samples, and is smaller for even parity. This result suggests that this even-odd behaviour found previously in the presence of electron correlations may be unrelated to charging effects in the sample. PACS numbers: 73.25.-b, 74.25.Fy, 73.63.Kv Since the pioneering work of Anderson, [1] localization in disordered systems has become a key issue in solid state physics. Mott and Twose [2] suggested that all the electronic eigenstates in less than two-dimensional disordered systems are localized. Borland [3] gave a rather general proof of this statement. Economou and Cohen [4] have re-examined the localization problem in the 1D tight-binding model, concluding that all states are localized if and only if the nearest-neighbor coupling is considered. However, Theodorou and Cohen [5] showed that the state at the middle of the band is extended, regardless of the randomness of the nearest-neighbor hopping matrix elements. Recently, it has also been argued that the delocalization transition exists in1D systems with correlated diagonal and/or non-diagonal disorder, i.e., that at some particular energies the states are extended. [6] The delocalization transition has now been investigated in 1D random quantum Ising chains [7], 1D random XY models [8], weakly disordered quasi 1D tight-binding hopping models [9] and dirty superconducting wires. [10].