Anomalous Localization and Mobility Edges in Non-Hermitian Quasicrystals with Disordered Imaginary Gauge Fields
Pith reviewed 2026-05-16 12:33 UTC · model grok-4.3
The pith
A Bernoulli imaginary gauge field in a non-Hermitian Aubry-André-Harper chain produces an anomalous transition from erratic skin-effect states to fully localized states.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
In the nearest-neighbor limit the model exhibits an anomalous transition from a fully erratic non-Hermitian skin effect phase to a fully localized phase. Although the fractal dimension vanishes on both sides of the transition, the Lyapunov exponent and the variance of the eigenstate center of mass sharply distinguish the two regimes. With weak next-nearest-neighbor hopping the transition point functions as a mobility edge separating Anderson-localized states from ENHSE-type states whose spectral winding and wave-packet dynamics differ from those of the Hermitian generalized Aubry-André-Harper model.
What carries the argument
The one-dimensional non-Hermitian Aubry-André-Harper chain with Bernoulli-distributed imaginary gauge field, whose nearest-neighbor limit hosts the ENHSE-to-localized transition diagnosed by Lyapunov exponents and center-of-mass fluctuations.
If this is right
- The transition coincides with a change from complex to real eigenvalues under periodic boundary conditions.
- Spectral winding number changes from nontrivial to trivial across the transition.
- The anomalous mobility edge remains at the same parameter location as the Hermitian generalized Aubry-André-Harper mobility edge.
- Single disorder realizations display winding-dependent wave-packet drift while full disorder averaging restores Hermitian-like transport.
Where Pith is reading between the lines
- Replacing the Bernoulli distribution with a smooth random distribution would likely smear the sharp distinction between the two phases.
- The same Lyapunov-exponent and center-of-mass diagnostics could be applied to two-dimensional non-Hermitian quasicrystals to look for analogous anomalous mobility edges.
- Cold-atom or photonic-lattice experiments with engineered gain-loss profiles could directly measure the predicted winding-dependent drift of wave packets.
Load-bearing premise
The transition and mobility edge rely on the imaginary gauge field obeying a Bernoulli distribution and on strictly nearest-neighbor hopping; any other distribution or longer-range hopping can remove the anomalous character.
What would settle it
Compute the Lyapunov exponent and center-of-mass fluctuation across the critical point for many finite realizations in the nearest-neighbor model; if these quantities vary continuously rather than jump, the claimed anomalous transition is ruled out.
Figures
read the original abstract
Localization in non-Hermitian quasicrystals can differ fundamentally from its Hermitian counterpart when non-reciprocity is spatially disordered. Here we study a one-dimensional non-Hermitian Aubry-Andr\'{e}-Harper chain with a Bernoulli imaginary gauge field and quasiperiodic onsite modulation. In the nearest-neighbor limit, we identify an anomalous transition from a fully erratic non-Hermitian skin effect (ENHSE) phase to a fully localized phase. Although the fractal dimension vanishes in both regimes, the Lyapunov exponent and the fluctuation of the eigenstate center of mass sharply distinguish them. For generic finite-size realizations, this transition is further accompanied by a complex-to-real spectral change under periodic boundary conditions and a change of spectral winding from nontrivial to trivial. With weak next-nearest-neighbor hopping, we uncover an anomalous mobility edge at the same location as in the Hermitian generalized Aubry-Andr\'{e}-Harper model, but separating Anderson-localized states from ENHSE-type macroscopic-accumulation states rather than extended states. We further show that this anomalous localization structure is reflected in spectral winding and wave-packet dynamics: single realizations exhibit winding-dependent drift, winding-resolved averaging preserves opposite directional responses, and full disorder averaging largely restores Hermitian-like transport. Our results establish practical diagnostics of anomalous localization and mobility edges in non-Hermitian quasicrystals.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This paper examines a non-Hermitian Aubry-André-Harper chain with a Bernoulli imaginary gauge field and quasiperiodic onsite modulation. In the nearest-neighbor limit, it identifies an anomalous transition from a fully erratic non-Hermitian skin effect (ENHSE) phase to a fully localized phase. Although the fractal dimension vanishes in both regimes, the phases are distinguished by the Lyapunov exponent and eigenstate center-of-mass fluctuation. The transition is accompanied by a complex-to-real spectral change and a change in spectral winding from nontrivial to trivial under periodic boundaries. With weak next-nearest-neighbor hopping, an anomalous mobility edge appears at the same location as in the Hermitian case but separates Anderson-localized states from ENHSE-type states. The work further connects these features to spectral winding and wave-packet dynamics under different averaging schemes.
Significance. If the reported distinctions survive the thermodynamic limit, the manuscript would provide useful, independently defined diagnostics (Lyapunov exponent, center-of-mass fluctuation, spectral winding) for identifying anomalous localization phases in non-Hermitian quasicrystals that differ from both Hermitian Anderson localization and conventional skin-effect phenomenology. The explicit links to wave-packet dynamics and averaging procedures add practical value for experimental realization.
major comments (1)
- [Abstract and nearest-neighbor results section] Abstract and nearest-neighbor results section: the central claim that the Lyapunov exponent and eigenstate center-of-mass fluctuation sharply distinguish the ENHSE phase from the localized phase rests on data for generic finite-size realizations. No explicit finite-size scaling analysis or L→∞ extrapolation of either quantity is presented, leaving open the possibility that the apparent sharpness is a finite-size artifact arising from the 'erratic' character of the skin effect.
minor comments (2)
- [Abstract] The acronym ENHSE is introduced in the abstract without expansion; spell out 'erratic non-Hermitian skin effect' on first use and ensure consistent definition in the main text.
- [Methods or numerical details section] Clarify the precise numerical definition of the eigenstate center-of-mass fluctuation (e.g., variance formula) and the system sizes used for the reported Lyapunov exponents to aid reproducibility.
Simulated Author's Rebuttal
We thank the referee for the careful reading of our manuscript and the constructive comments. We address the major concern regarding finite-size effects below and have revised the manuscript to include additional analysis.
read point-by-point responses
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Referee: [Abstract and nearest-neighbor results section] Abstract and nearest-neighbor results section: the central claim that the Lyapunov exponent and eigenstate center-of-mass fluctuation sharply distinguish the ENHSE phase from the localized phase rests on data for generic finite-size realizations. No explicit finite-size scaling analysis or L→∞ extrapolation of either quantity is presented, leaving open the possibility that the apparent sharpness is a finite-size artifact arising from the 'erratic' character of the skin effect.
Authors: We agree that the distinction between the ENHSE and localized phases would be more robustly established with explicit finite-size scaling. The current results are shown for finite L with multiple generic realizations, where the Lyapunov exponent and center-of-mass fluctuation exhibit a clear jump at the transition. To address the concern directly, the revised manuscript adds a finite-size scaling analysis (new figure and discussion in the nearest-neighbor section) for L up to several hundred sites. This confirms that the sharpness persists without rounding as L increases, with the Lyapunov exponent remaining near zero on the ENHSE side and acquiring a finite value on the localized side, and the fluctuation showing a corresponding drop. The transition location is stable under this scaling, indicating it is not a finite-size artifact. We have also updated the abstract to note the added scaling support. revision: yes
Circularity Check
No significant circularity; central diagnostics are independently defined
full rationale
The paper identifies the ENHSE-to-localized transition and anomalous mobility edge via direct numerical evaluation of the Lyapunov exponent, eigenstate center-of-mass fluctuation, fractal dimension, spectral winding, and wave-packet dynamics. None of these quantities is defined in terms of the transition location or fitted to it; the fractal dimension vanishing on both sides is reported as an observation, not a redefinition. No load-bearing self-citation chain or ansatz smuggling is required for the distinction, and the nearest-neighbor Bernoulli case is treated as a specific parameter regime rather than a tautological input. The derivation chain therefore remains self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
free parameters (1)
- imaginary gauge field amplitude
axioms (1)
- domain assumption The Lyapunov exponent and eigenstate center-of-mass fluctuation are independent of the fractal dimension and can be used to distinguish phases when the latter vanishes.
invented entities (1)
-
erratic non-Hermitian skin effect (ENHSE)
no independent evidence
Lean theorems connected to this paper
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IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
We employ a non-unitary gauge transformation... γ_NH(En) ≃ γ_H(En). This mapping allows us to determine the localization transitions using known results from the Hermitian AAH models
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IndisputableMonolith/Foundation/AlphaCoordinateFixation.leanJ_uniquely_calibrated_via_higher_derivative unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
the Lyapunov exponent undergoes a transition from zero to finite at λ=2... fractal dimension D→0 in both phases
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Forward citations
Cited by 1 Pith paper
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Erratic Liouvillian Skin Localization and Subdiffusive Transport
Globally reciprocal Liouvillian systems show erratic localization coexisting with subdiffusive transport, unlike ballistic transport in equivalent Hamiltonian models.
Reference graph
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discussion (0)
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