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 (Wc), which is equal to the incident energy (E), below which the localization length ξ decreases with the random strength W for a fixed incident angle θ. But the localization length drops abruptly to a minimum at W=Wc and rises immediately afterward. The incident angle dependence of the localization length has different asymptotic behaviors in the two regions of random strength, with ξ∝sin−4θ when W<Wc and ξ∝sin−2θ when W>Wc. The existence of a sharp transition at W=Wc is due to the emergence of evanescent waves in the systems when W>Wc. 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 θ dependence of the localization length has the same asymptotic behavior ξ∝sin−2θ.