Prof. Kousuke Yakubo (Department of Applied Physics, Hokkaido University)
"Gradon Localization in Graded Systems"
We have identified new types of transition from extended to localized excitations in various graded systems in which parameters characterizing systems vary linearly in a longitudinal direction. In a one-dimensional graded elastic chain, we found that the delocalization transition occurs at the maximum frequency of the corresponding homogeneous chain, which is in a continuous single band. Although each state in the localized phase, called gradon, can be regarded as a impurity localized mode, the localization profile is clearly distinct from usual impurity modes or the Anderson localized modes. We also show several types of gradons in higher dimensional graded elastic networks. Furthermore, we clarified that there exist plasmonic gradons in graded plasmonic crystals in which noble metal nanoparticles embedded in a graded dielectric medium. Gradons provide a rich variation of excitation modes in various graded systems and can be utilized for many applications.