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1. Density of States and Delocalization for Discrete Magnetic Random Schrödinger Operators

   https://doi.org/10.1093/imrn/rnab017  

   Becker, Simon; Han, Rui (May 2021, International Mathematics Research Notices)

   Abstract We study discrete magnetic random Schrödinger operators on the square and honeycomb lattice. For the non-random magnetic operator on the hexagonal lattice with any rational magnetic flux, we show that the middle two dispersion surfaces exhibit Dirac cones. We then derive an asymptotic expansion for the density of states on the honeycomb lattice for oscillations of arbitrary rational magnetic flux. This allows us, as a corollary, to rigorously study the quantum Hall effect and conclude dynamical delocalization close to the conical point under disorder. We obtain similar results for the discrete random Schrödinger operator on the $$\mathbb Z^2$$-lattice with weak magnetic fields, close to the bottom and top of its spectrum. 

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2. On Strichartz estimates for many-body Schrödinger equation in the periodic setting

   https://doi.org/10.1515/forum-2024-0105  

   Huang, Xiaoqi; Yu, Xueying; Zhao, Zehua; Zheng, Jiqiang (May 2024, Forum Mathematicum)

   Abstract In this paper, we prove Strichartz estimates for many body Schrödinger equations in the periodic setting, specifically on tori ${𝕋}^d${\mathbb{T}^{d}}, where $d\ge 3${d\geq 3}. The results hold for both rational and irrational tori, and for small interacting potentials in a certain sense. Our work is based on the standard Strichartz estimate for Schrödinger operators on periodic domains, as developed in [J. Bourgain and C. Demeter,The proof of the $l^2$l^{2}decoupling conjecture,Ann. of Math. (2) 182 2015, 1, 351–389]. As a comparison, this result can be regarded as a periodic analogue of [Y. Hong,Strichartz estimates forN-body Schrödinger operators with small potential interactions,Discrete Contin. Dyn. Syst. 37 2017, 10, 5355–5365] though we do not use the same perturbation method. We also note that the perturbation method fails due to the derivative loss property of the periodic Strichartz estimate. 

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3. Sharp decay rate for eigenfunctions of perturbed periodic Schrödinger operators

   https://doi.org/10.1088/1361-6544/adc653  

   Liu, Wencai; Matos, Rodrigo; Treuer, John N (April 2025, Nonlinearity)

   Abstract This paper investigates uniqueness results for perturbed periodic Schrödinger operators on ${\mathbb{Z}}^d$. Specifically, we consider operators of the form $H=-\mathrm{\Delta }+V+v$, where Δ is the discrete Laplacian, $V:{\mathbb{Z}}^d\to \mathbb{R}$is a periodic potential, and $v:{\mathbb{Z}}^d\to \mathbb{C}$represents a decaying impurity. We establish quantitative conditions under which the equation $-\mathrm{\Delta }u+Vu+vu=\lambda u$, for $\lambda \in \mathbb{C}$, admits only the trivial solution $u\equiv 0$. Key applications include the absence of embedded eigenvalues for operators with impurities decaying faster than any exponential function and the determination of sharp decay rates for eigenfunctions. Our findings extend previous works by providing precise decay conditions for impurities and analyzing different spectral regimes ofλ. 

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4. On the number of closed gaps of discrete periodic one-dimensional operators

   https://doi.org/10.1063/5.0175428  

   Arroyo, Andrew; Castro, Faye; Fillman, Jake (May 2024, Journal of Mathematical Physics)

   From the general inverse theory of periodic Jacobi matrices, it is known that a periodic Jacobi matrix of minimal period p≥2 may have at most p−2 closed spectral gaps. We discuss the maximal number of closed gaps for one-dimensional periodic discrete Schrödinger operators of period p. We prove nontrivial upper and lower bounds on this quantity for large p and compute it exactly for p≤6. Among our results, we show that a discrete Schrödinger operator of period four or five may have at most a single closed gap, and we characterize exactly which potentials may exhibit a closed gap. For period six, we show that at most two gaps may close. In all cases in which the maximal number of closed gaps is computed, it is seen to be strictly smaller than p−2, the bound guaranteed by the inverse theory. We also discuss similar results for purely off-diagonal Jacobi matrices. 

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5. Anderson localization for Schrödinger operators with monotone potentials over circle homeomorphisms

   https://doi.org/10.4171/JST/531  

   Kerdboon, Jiranan; Zhu, Xiaowen (October 2024, Journal of Spectral Theory)

   In this paper, we prove pure point spectrum for a large class of Schrödinger operators over circle maps with conditions on the rotation number going beyond the Diophantine. More specifically, we develop the scheme to obtain pure point spectrum for Schrödinger operators with monotone bi-Lipschitz potentials over orientation-preserving circle homeomorphisms with Diophantine or weakly Liouville rotation number. The localization is uniform when the coupling constant is large enough. 

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