Localization dichotomy for non-periodic gapped systems

Let PP be an orthogonal projector that admits an exponentially localized kernel. A generalized Wannier basis for PP is an orthonormal basis of range(P)\operatorname{range}(P); it is ss-localized if there are center points μαR2\boldsymbol{\mu}_{\alpha}\in\mathbb{R}^2 and a finite constant CC such that

R2xμα2sψα(x)2dxC\int_{\mathbb{R}^2} \langle \boldsymbol{x}-\boldsymbol{\mu}_{\alpha}\rangle^{2s}|\psi_{\alpha}(\boldsymbol{x})|^2\,d\boldsymbol{x}\leq C

for every basis element, where xμα=(xμα2+1)1/2\langle \boldsymbol{x}-\boldsymbol{\mu}_{\alpha}\rangle=(|\boldsymbol{x}-\boldsymbol{\mu}_{\alpha}|^2+1)^{1/2}. The Chern marker C(P)C(P) is the thermodynamic-limit invariant defined for PP.

Localization dichotomy conjecture. The following statements are equivalent: (a) PP admits a generalized Wannier basis that is exponentially localized; (b) PP admits a generalized Wannier basis that is ss-localized for s=1s=1; (c) PP is topologically trivial in the sense that its Chern marker C(P)C(P) exists and equals zero.

This conjecture extends the periodic localization dichotomy to non-periodic gapped systems. It identifies exponential localization, finite second moment, and vanishing Chern marker as equivalent conditions; the supplied text gives no resolution status.

Sources & referencesView supporting material

Primary source

Jianfeng Lu and Kevin D. Stubbs, “Algebraic localization of Wannier functions implies Chern triviality in non-periodic insulators”, arXiv:2107.10699 (2021).

Additional references

2 papers in this index state this conjecture (2020–2021). The statement above is taken from the most recent of them; the others are arXiv:2012.14407.

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