Matryoshka approach to Sine-Cosine topological models

Abstract

We address a particular set of extended Su-Schrieffer-Heeger models with $2n$ sites in the unit cell [SSH($2n$)], that we designate by Sine-Cosine models [SC$(n)$], with hopping terms defined as a sequence of $n$ sine-cosine pairs of the form $\{\sin ({\theta }_j),\cos ({\theta }_j)\}$, $j=1,\cdots ,n$. These models, when squared, generate a block-diagonal matrix representation with one of the blocks corresponding to a chain with uniform local potentials. We further focus our study on the subset of SC$(2^{n-1})$ chains that, when squared an arbitrary number of times (up to $n$), always generate a block which is again a Sine-Cosine model, if an energy shift is applied and if the energy unit is renormalized. We show that these $n$-times squarable models [SSC$(n)$] and their band structure are uniquely determined by the sequence of energy unit renormalizations and by the energy shifts associated to each step of the squaring process. Chiral symmetry is present in all Sine-Cosine chains and edge states levels at the respective central gaps are protected by it. Zero-energy edge states in a SSC$(j)$ chain (with $j<n$) of the Matryoshka sequence obtained squaring the SSC$(n)$ chain with open boundary conditions (OBC), become finite energy edge states in non-central band gaps of the SSC$(n)$ chain. The extension to higher dimensions is discussed.

7 pages, 5 figures

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• One-dimensional $2^n$-root topological insulators and superconductors
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• Square-root Floquet topological phases and time crystals
• Long-range hopping and indexing assumption in one-dimensional topological insulators
• Kaleidoscopes of Hofstadter Butterflies and Aharonov-Bohm caging from $2^n$-root topology in decorated square lattices
• Higher-Order Topological Insulator on a Martini Lattice and Its Square Root Descendant
• Supersymmetry on the lattice: Geometry, Topology, and Flat Bands
• Topological $n$-root Su-Schrieffer-Heeger model in a non-Hermitian photonic ring system
• Generalized Lieb's theorem for noninteracting non-Hermitian $n$-partite tight-binding lattices
• Kitaev Chain with a Fractional Twist
• Exceptionally deficient topological square-root insulators
• High-root topological edge-state bands
• $q$th-root non-Hermitian Floquet topological insulators
• Realization of second-order photonic square-root topological insulators
• Exceptional horns in $n$-root graphene and Lieb photonic ring lattices