On a question of Hof, Knill and Simon on palindromic substitutive systems
: Harju T, Vesti J, Zamboni LQ
Publisher: SPRINGER WIEN
: 2016
: Monatshefte für Mathematik
: MONATSHEFTE FUR MATHEMATIK
: MONATSH MATH
: 179
: 3
: 379
: 388
: 10
: 0026-9255
DOI: https://doi.org/10.1007/s00605-015-0828-2
In a 1995 paper, Hof et al. obtain a sufficient combinatorial criterion on the subshift Omega of the potential of a discrete Schrdinger operator which guarantees purely singular continuous spectrum on a generic subset of Omega. In part, this condition requires that the subshift Omega be palindromic, i.e., contains an infinite number of distinct palindromic factors. In the same paper, they introduce the class P of morphisms f : A* -> B* of the form a bar right arrow pq(a) with p and q(a) palindromes, and ask whether every palindromic subshift generated by a primitive substitution arises from morphisms of class P or by morphisms of the form a bar right arrow q(a) p. In this paperwegive a partial affirmative answer to the question of Hof et al.: we show that every rich primitive substitutive subshift is generated by at most two morphisms each of which is conjugate to a morphism of class P. More precisely, we show that every rich (or almost rich in the sense of finite defect) primitive morphic word y is an element of B-omega is of the form y = f (x) where f : A* -> B* is conjugate to a morphism of class P, and where x is a rich word fixed by a primitive substitution g : A* -> A* conjugate to one in class P.