Quantum lattice transport along an infinitely extended perturbation

Quantum lattice transport along an infinitely extended perturbation

Summary

The paper studies the quantum lattice transport along an infinitely extended perturbation, analyzing the band spectrum of a periodic quantum graph with a δ-coupling of strength γ in the vertices perturbed by changing the latter at an infinite straight array of vertices to a γ ̸= γ.

Highlights

  • The authors consider a periodic quantum graph in the form of a rectangular lattice with a δ-coupling of strength γ in the vertices.
  • The perturbation is introduced by changing the coupling strength to γ ̸= γ at an infinite straight array of vertices.
  • The spectrum of the unperturbed system is analyzed using the Floquet-Bloch theory.
  • The authors prove that the spectrum remains preserved as a set provided γ ̸= γ > 0.
  • For all other combinations, additional bands appear in some or all gaps of the unperturbed system.
  • The probability of existence of a state exponentially localized in the vicinity of the perturbation equals 1.
  • The high-energy behavior of the spectrum is also analyzed.

Key Insights

  • The authors use the Floquet-Bloch theory to analyze the spectrum of the unperturbed system, which is a powerful tool for studying periodic systems.
  • The introduction of the perturbation leads to the appearance of new spectral bands, which can be analyzed using the band conditions derived in the paper.
  • The authors prove that the spectrum remains preserved as a set provided γ ̸= γ > 0, which is an interesting result that sheds light on the behavior of the system under perturbation.
  • The high-energy behavior of the spectrum is also analyzed, and the authors show that the probability of existence of a state exponentially localized in the vicinity of the perturbation equals 1.
  • The paper provides a detailed analysis of the band-gap structure of the spectrum, which is an important aspect of quantum systems.
  • The authors use a combination of analytical and numerical methods to study the system, which provides a comprehensive understanding of the behavior of the system.
  • The results of the paper have implications for the study of quantum transport in periodic systems, which is an active area of research in condensed matter physics.

Mindmap

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Rectangular lattice with δ-coupling at vertices
Perturbation changes coupling constant along chain
Band-gap structure of spectrum
Quantum Lattice Transport
Absolutely continuous bands and flat bands
Finite number of open gaps
Infinitely many gaps accumulate at infinity
Spectrum of Unperturbed System
Positive part has band-gap structure
Negative part has at most one band
Flat bands at edges of ac bands
Properties of Unperturbed Spectrum
Periodic in direction parallel to perturbation
Floquet-Bloch decomposition along this direction
New spectral bands in gaps of σ(Hγ)
Perturbed System
Band conditions (3.25) and (3.26)
Gap conditions (3.36) and (3.37)
Behavior of g±(τ;k) in gaps
Conditions for New Spectral Bands
Spectrum dominated by bands
Infinite number of bands
Band widths asymptotically bounded
High-Energy Regime
Probability of belonging to Sγ,γ˜
Conditions (4.3) and (4.4)
Probabilities p1 and p2
Probability of Belonging to Spectral Bands
Type (I) and type (II) behavior
Functions g±(τ;k) tend to ±∞
Functions g±(τ;k) reach finite values
Behavior of g±(τ;k) at Band Edges
Greater or less than γ
Dependence on sinka and sinkb
Conditions for touching band edges
Properties of γp± and γp∓
Single negative band
Behavior of g(98)±(τ;κ)
Conditions for touching band edges
Negative Spectrum
No gap closure
Behavior of g±(τ;k) at band edges
Exception for Square Lattice
Probability equal to 1
Conditions (4.3) and (4.4)
Probabilities p1 and p2
Probability of Belonging to Sγ,γ˜

Citation

Baradaran, M., Exner, P., & Khrabustovskyi, A. (2024). Quantum lattice transport along an infinitely extended perturbation (Version 1). arXiv. https://doi.org/10.48550/ARXIV.2412.20919

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