String and conventional order parameters in the solvable modulated quantum chain

Abstract

The phase diagram and the order parameters of the exactly solvable quantum 1D model are analysed. The model in its spin representation is the dimerized XY spin chain in the presence of uniform and staggered transverse fields. In the fermionic representation this model is the dimerized non-interacting Kitaev chain with a modulated chemical potential. The model has a rich phase diagram which contains phases with local and non-local (string) orders. We have calculated within the same systematic framework the local order parameters (spontaneous magnetization) and the non-local string order parameters, along with the topological winding numbers for all domains of the phase diagram. The topologically nontrivial phase is shown to have a peculiar oscillating string order with the wavenumber $q=\pi/2$, awaiting for its experimental confirmation.