Anisotropic optical conductivity of decagonal quasicrystals

The optical conductivity of high quality decagonal quasicrystals of ${\mathrm{Al}}_{65}$ ${\mathrm{Co}}_{17}$ ${\mathrm{Cu}}_{18}$ and ${\mathrm{Al}}_{62}$ ${\mathrm{Co}}_{15}$ ${\mathrm{Cu}}_{20}$ ${\mathrm{Si}}_3$ shows a strong anisotropy between the periodic and the quasiperiodic directions. We suggest that this is due to the dramatic enhancement of scattering in the quasiperiodic planes. The analysis of the conductivity reveals a drastic difference between the electronic structure of the decagonal quasicrystals and the icosahedral quasicrystals.