Persistence of Unitary Almost Mathieu Operator Gaps Ten Dry Martinis, Five on the Rim

We determine exactly which gap labels are realized by open spectral gaps for the unitary almost Mathieu operator at every irrational frequency and all coupling constants ($0<λ_1,λ_2\leq1$). When both couplings are strictly less than one, every permitted gap label is realized by an open gap, including in the critical case ($λ_1=λ_2$). When at least one coupling equals one, both lifts of every odd winding label are realized by open gaps, whereas all even winding labels are collapsed. The proof combines quantitative almost reducibility and Aubry duality with a monotonicity principle for gap heights.

Source: arXiv:2610.42120v1 - http://arxiv.org/abs/2610.42120v1 PDF: https://arxiv.org/pdf/2610.42120v1 Original Link: http://arxiv.org/abs/2610.42120v1