Existence of only delocalized eigenstates in the electronic spectrum of the Thue–Morse lattice

We present an analytical method for finding all the electronic eigenfunctions and eigenvalues of the aperiodic Thue–Morse lattice. We prove that this system supports only extended electronic states which is a very unusual behavior for this class of systems, and so far as we know, this is the only example of a quasiperiodic or aperiodic system in which critical or localized states are totally absent in the spectrum. Interestingly, we observe that the symmetry of the lattice leads to the existence of degenerate eigenstates and all the eigenvalues excepting the four global band edges are doubly degenerate. We show exactly that the Landauer resistivity is zero for all the degenerate eigenvalues and it scales as L2 (L=systemsize) at the global band edges. We also find that the localization length ξ diverges in the limit of infinite system size.