Regensburg 2025 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 5: Statistical Physics: General

DY 5.1: Talk

Monday, March 17, 2025, 09:30–09:45, H47

The scaling behaviour of localised and extended states in one-dimensional tight-binding models with disorder — •Luca Schaefer and Barbara Drossel — Technische Universität Darmstadt, Hochschulstraße 6, 64289 Darmstadt

We investigate two one-dimensional tight-binding models with disorder that have extended states at zero energy. We use the eigenmodes of the Hamiltonian and the associated participation ratios, and the transfer-matrix method to determine the localisation length. The first model has no on-site disorder, but random couplings. While the participation ratio remains finite at zero energy, the localisation length diverges logarithmically as the energy goes to zero. We provide an intuitive derivation of this logarithmic divergence based on the weak coupling of the two sublattices. The second model has a conserved quantity as the row sums of the Hamiltonian are zero. This model can be represented as a harmonic chain with random couplings, or as a diffusion model on a lattice with random links. We find, in agreement with existing analytical calculations, that the number of system-spanning eigenmodes increases proportionally to the square root of the system size, and we related this power law to other power laws that characterise the scaling behaviour of the eigenmodes, the participation ratio, the localisation length, and their dependence on energy and system size. When disorder is so strong that the smallest hopping terms can be arbitrarily close to zero, all these power laws change, and we show a crossover between the two scaling regimes. All these results are explained by intuitive arguments based on scaling.

Keywords: Anderson Localization; Disordered Systems; Tight-binding model