title: Anomalous Anderson localization behaviors in disordered pseudospin systems.
abstract: We discovered unique Anderson localization behaviors of pseudospin systems in a 1D disordered potential. For a pseudospin-1 system, due to the absence of backscattering under normal incidence and the presence of a conical band structure, the wave localization behaviors are entirely different from those of conventional disordered systems. We show that there exists a critical strength of random potential ([Formula: see text]), which is equal to the incident energy ([Formula: see text]), below which the localization length [Formula: see text] decreases with the random strength [Formula: see text] for a fixed incident angle [Formula: see text] But the localization length drops abruptly to a minimum at [Formula: see text] and rises immediately afterward. The incident angle dependence of the localization length has different asymptotic behaviors in the two regions of random strength, with [Formula: see text] when [Formula: see text] and [Formula: see text] when [Formula: see text] The existence of a sharp transition at [Formula: see text] is due to the emergence of evanescent waves in the systems when [Formula: see text] Such localization behavior is unique to pseudospin-1 systems. For pseudospin-1/2 systems, there is also a minimum localization length as randomness increases, but the transition from decreasing to increasing localization length at the minimum is smooth rather than abrupt. In both decreasing and increasing regions, the [Formula: see text] dependence of the localization length has the same asymptotic behavior [Formula: see text].
authors.affiliation: Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.|Institute for Advanced Study, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
authors.forename: A
authors.identifier: 0000-0002-9162-1915
authors.initials: A
authors.lastname: Fang
authors.affiliation: Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.|Institute for Advanced Study, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
authors.forename: Z Q
authors.initials: ZQ
authors.lastname: Zhang
authors.affiliation: Institute for Advanced Study, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.|Department of Physics, University of California, Berkeley, CA 94720.|Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
authors.forename: Steven G
authors.initials: SG
authors.lastname: Louie
authors.affiliation: Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China; phchan@ust.hk.|Institute for Advanced Study, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
authors.forename: C T
authors.initials: CT
authors.lastname: Chan
keywords: disorder; evanescent waves; localization; photonic crystals; pseudospin