Coexistence of 1D and 2D topology and genesis of Dirac cones in the chiral Aubry-Andr\'e model

Abstract

We construct a one-dimensional (1D) topological SSH-like model with chiral symmetry and a superimposed hopping modulation, which we call the chiral Aubry-Andr\'e model. We show that its topological properties can be described in terms of a pair (C,W) of a two-dimensional (2D) Chern number C, stemming from a superspace description of the model, and a 1D winding number W, originating in its chiral symmetric nature. Thus, we showcase for the first time explicit coexistence of 1D and 2D topology in a model existing in 1D physical space. We detail the superspace description by showcasing how our model can be mapped to a Harper-Hofstadter model, familiar from the description of the integer quantum Hall effect, and analyze the vanishing field limit analytically. An extension of the method used for vanishing fields is provided in order to handle any finite fields, corresponding to hopping modulations both commensurate and incommensurate with the lattice. In addition, this formalism allows us to obtain certain features of the 2D superspace model, such as its number of massless Dirac nodes, purely in terms of topological quantities, computed without the need to go into momentum space.