@article{6086,
abstract = {We show that linear analytic cocycles where all Lyapunov exponents are negative infinite are nilpotent. For such one-frequency cocycles we show that they can be analytically conjugated to an upper triangular cocycle or a Jordan normal form. As a consequence, an arbitrarily small analytic perturbation leads to distinct Lyapunov exponents. Moreover, in the one-frequency case where the th Lyapunov exponent is finite and the st negative infinite, we obtain a simple criterion for domination in which case there is a splitting into a nilpotent part and an invertible part.},
author = {Sadel, Christian and Xu, Disheng},
journal = {Ergodic Theory and Dynamical Systems},
number = {4},
pages = {1082--1098},
publisher = {Cambridge University Press},
title = {{Singular analytic linear cocycles with negative infinite Lyapunov exponents}},
doi = {10.1017/etds.2017.52},
volume = {39},
year = {2019},
}
@article{1257,
abstract = {We consider products of random matrices that are small, independent identically distributed perturbations of a fixed matrix (Formula presented.). Focusing on the eigenvalues of (Formula presented.) of a particular size we obtain a limit to a SDE in a critical scaling. Previous results required (Formula presented.) to be a (conjugated) unitary matrix so it could not have eigenvalues of different modulus. From the result we can also obtain a limit SDE for the Markov process given by the action of the random products on the flag manifold. Applying the result to random Schrödinger operators we can improve some results by Valko and Virag showing GOE statistics for the rescaled eigenvalue process of a sequence of Anderson models on long boxes. In particular, we solve a problem posed in their work.},
author = {Sadel, Christian and Virág, Bálint},
journal = {Communications in Mathematical Physics},
number = {3},
pages = {881 -- 919},
publisher = {Springer},
title = {{A central limit theorem for products of random matrices and GOE statistics for the Anderson model on long boxes}},
doi = {10.1007/s00220-016-2600-4},
volume = {343},
year = {2016},
}
@article{1223,
abstract = {We consider a random Schrödinger operator on the binary tree with a random potential which is the sum of a random radially symmetric potential, Qr, and a random transversally periodic potential, κQt, with coupling constant κ. Using a new one-dimensional dynamical systems approach combined with Jensen's inequality in hyperbolic space (our key estimate) we obtain a fractional moment estimate proving localization for small and large κ. Together with a previous result we therefore obtain a model with two Anderson transitions, from localization to delocalization and back to localization, when increasing κ. As a by-product we also have a partially new proof of one-dimensional Anderson localization at any disorder.},
author = {Froese, Richard and Lee, Darrick and Sadel, Christian and Spitzer, Wolfgang and Stolz, Günter},
journal = {Journal of Spectral Theory},
number = {3},
pages = {557 -- 600},
publisher = {European Mathematical Society},
title = {{Localization for transversally periodic random potentials on binary trees}},
doi = {10.4171/JST/132},
volume = {6},
year = {2016},
}
@article{1608,
abstract = {We show that the Anderson model has a transition from localization to delocalization at exactly 2 dimensional growth rate on antitrees with normalized edge weights which are certain discrete graphs. The kinetic part has a one-dimensional structure allowing a description through transfer matrices which involve some Schur complement. For such operators we introduce the notion of having one propagating channel and extend theorems from the theory of one-dimensional Jacobi operators that relate the behavior of transfer matrices with the spectrum. These theorems are then applied to the considered model. In essence, in a certain energy region the kinetic part averages the random potentials along shells and the transfer matrices behave similar as for a one-dimensional operator with random potential of decaying variance. At d dimensional growth for d>2 this effective decay is strong enough to obtain absolutely continuous spectrum, whereas for some uniform d dimensional growth with d<2 one has pure point spectrum in this energy region. At exactly uniform 2 dimensional growth also some singular continuous spectrum appears, at least at small disorder. As a corollary we also obtain a change from singular spectrum (d≤2) to absolutely continuous spectrum (d≥3) for random operators of the type rΔdr+λ on ℤd, where r is an orthogonal radial projection, Δd the discrete adjacency operator (Laplacian) on ℤd and λ a random potential. },
author = {Sadel, Christian},
journal = {Annales Henri Poincare},
number = {7},
pages = {1631 -- 1675},
publisher = {Birkhäuser},
title = {{Anderson transition at 2 dimensional growth rate on antitrees and spectral theory for operators with one propagating channel}},
doi = {10.1007/s00023-015-0456-3},
volume = {17},
year = {2016},
}
@article{1503,
abstract = {A Herman-Avila-Bochi type formula is obtained for the average sum of the top d Lyapunov exponents over a one-parameter family of double-struck G-cocycles, where double-struck G is the group that leaves a certain, non-degenerate Hermitian form of signature (c, d) invariant. The generic example of such a group is the pseudo-unitary group U(c, d) or, in the case c = d, the Hermitian-symplectic group HSp(2d) which naturally appears for cocycles related to Schrödinger operators. In the case d = 1, the formula for HSp(2d) cocycles reduces to the Herman-Avila-Bochi formula for SL(2, ℝ) cocycles.},
author = {Sadel, Christian},
journal = {Ergodic Theory and Dynamical Systems},
number = {5},
pages = {1582 -- 1591},
publisher = {Cambridge University Press},
title = {{A Herman-Avila-Bochi formula for higher-dimensional pseudo-unitary and Hermitian-symplectic-cocycles}},
doi = {10.1017/etds.2013.103},
volume = {35},
year = {2015},
}
@article{1926,
abstract = {We consider cross products of finite graphs with a class of trees that have arbitrarily but finitely long line segments, such as the Fibonacci tree. Such cross products are called tree-strips. We prove that for small disorder random Schrödinger operators on such tree-strips have purely absolutely continuous spectrum in a certain set.},
author = {Sadel, Christian},
journal = {Mathematical Physics, Analysis and Geometry},
number = {3-4},
pages = {409 -- 440},
publisher = {Springer},
title = {{Absolutely continuous spectrum for random Schrödinger operators on the Fibonacci and similar Tree-strips}},
doi = {10.1007/s11040-014-9163-4},
volume = {17},
year = {2014},
}