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arXiv · 2609.27324

Mobility-Gap Robustness and Středa-Hall Separation in Disordered Axion Pumping

Bryan Leung·Emil Prodan
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Abstract

We show that the noncommutative second Chern number of a $(3+1)$D disordered axion pump remains quantized beyond global spectral gap closure at $W_g \approx 14.5$. Large-scale computation of the second Chern number and finite-size scaling demonstrate convergence of $\mathrm{Ch}_2$ toward $-1$ well into the mobility-gap regime ($W \lesssim 16.5$), while the Středa-Hall response $\partial_ϕ\mathrm{Ch}_{0,3}$ departs rapidly after global spectral gap closure, serving as an internal control that distinguishes bulk mobility-gap protection from finite-size artifacts. Level statistics identify a 3D unitary Anderson transition at each pump slice and locate the mobility-edge bottleneck at $τ=0$, with critical disorder $W_c \approx 18$.

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Bryan Leung, Emil Prodan. 2026-09-23. Mobility-Gap Robustness and Středa-Hall Separation in Disordered Axion Pumping. https://arxiv.org/abs/2609.27324

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