Aharonov-Bohm cages, flat bands, and gap labeling in hyperbolic tilings

TL;DR

This paper explores Aharonov-Bohm cages and flat bands in hyperbolic tilings, revealing localization phenomena, complex spectra, and gap structures in negatively curved geometries, extending known Euclidean results to hyperbolic spaces.

Contribution

It demonstrates the existence of Aharonov-Bohm cages in hyperbolic dice tilings and analyzes their spectral properties, including Hofstadter butterflies and gap labeling, in hyperbolic geometries.

Findings

Aharonov-Bohm cages are present in hyperbolic dice tilings.

Hyperbolic Hofstadter butterflies lack Euclidean self-similarity but contain spectral gaps.

Hyperbolic kagome tilings exhibit highly degenerate states at specific magnetic fields.

Abstract

Aharonov-Bohm caging is a localization mechanism stemming from the competition between the geometry and the magnetic field. Originally described for a tight-binding model in the dice lattice, this destructive interference phenomenon prevents any wavepacket spreading away from a strictly confined region. Accordingly, for the peculiar values of the field responsible for this effect, the energy spectrum consists of a discrete set of highly degenerate flat bands. In the present work, we show that Aharonov-Bohm cages are also found in an infinite set of hyperbolic dice tilings defined on a negatively curved hyperbolic plane. We detail the construction of these tilings and compute their Hofstadter butterflies by considering periodic boundary conditions on high-genus surfaces. As recently observed for some regular hyperbolic tilings, these butterflies do not manifest the self-similar structure of their Euclidean counterparts but still contain some gaps. We also consider the energy spectrum of hyperbolic kagome tilings (which are the dual of hyperbolic dice tilings), which displays interesting features, such as highly degenerate states arising for some particular values of the magnetic field. For these two families of hyperbolic tilings, we compute the Chern number in the main gaps of the Hofstadter butterfly and propose a gap labeling inspired by the Euclidean case. Finally, we also study the triangular Husimi cactus, which is a limiting case in the family of hyperbolic kagome tilings, and we derive an exact expression for its spectrum versus magnetic flux.