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MON: Monday Contributed Sessions

MON 23: Poster Session: Fundamental Aspects and Model Systems

MON 23.42: Poster

Monday, September 8, 2025, 18:30–20:30, ZHG Foyer 1. OG

Spin and energy dynamics in the disordered spin-1/2 XX ladder — •Lukas Peinemann, Kadir Çeven, and Fabian Heidrich-Meisner — Institut für Theoretische Physik, Georg-August-Universität Göttingen, Germany

Understanding the relaxation dynamics of closed many-body quantum systems is a central goal in the study of non-equilibrium quantum physics. Within linear response theory, we numerically calculate the spin and energy diffusion coefficients in the disordered two-leg spin-1/2 XX ladder at infinite temperature, employing the concept of quantum typicality. Using exact diagonalization, we determine the disorder-induced finite-size crossover from delocalized to many-body localized regime by analyzing the gap ratio and the von Neumann entanglement entropy. We examine how the hierarchy of spin and energy diffusion constants in the delocalized regime compares to that in other non-integrable spin models, such as the XXZ chain with a staggered magnetic field. Our numerical findings reveal an atypical hierarchy in the XX ladder, where spin diffusion exceeds energy diffusion - in contrast to the behavior observed in the other studied models. This reversed hierarchy persists throughout the entire delocalized regime, with both diffusion constants decreasing systematically as disorder is increased. Moreover, our results suggest that increasing the inter-leg coupling leads to a convergence of the spin and energy diffusion coefficients.

We acknowledge funding from the Deutsche Forschungsgemeinschaft (German Research Foundation) within the research unit FOR5522 (Project No. 499180199)

Keywords: spin ladder; thermalization; relaxation; closed quantum systems; non-equilibrium quantum physics