9 August 2022 Tue 5 pm

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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 in a discrete set of highly degenerate flat bands. In this seminar, I will show that Aharonov-Bohm cages are also found in an infinite set of Dice-like tilings defined on a negatively curved hyperbolic plane [1]. The construction of these tilings and  their computed Hofstadter butterflies (by considering periodic boundary conditions) on high-genus surfaces will be detailed. 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 Kagome-like tilings (which are dual of Dice-like 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.

[1]  Aharonov-Bohm cages, flat bands, and gap labeling in hyperbolic tilings, R. Mosseri R. Vogeler and J. Vidal, arXiv: 2206.04543

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