Work

Fock-space fragmentation in quenches of disordered interacting fermions

Year: 2026

Type: article

Abstract: Fock-space fragmentation, as it is currently investigated, primarily originates from specific kinematic constraints or emergent conservation laws in many-body systems with translation invariance. It leads to nonergodic dynamics and possible breakdown of the eigenstate thermalization hypothesis. Here, we demonstrate that also in disordered systems, such as the XXZ model with random on-site fields, fragmentation appears as a natural concept offering fresh perspectives, for example, on many-body localization. Specifically, for a given quenched initial state, we identify a potential-energy shell in Fock space, defined by its energy and energy uncertainty, which represents the energetically accessible part of the many-body configuration space. For example, the drastic sample-to-sample fluctuations observed in the weak disorder regime, W < W frag , represent fluctuations of the mass of the shell. Upon increasing disorder, the potential-energy shell becomes increasingly fragmented. Its finite-size evolution exhibits a turnaround flow; extrapolating this flow to the disorder at which the turnaround vanishes provides a heuristic estimate of the strong-fragmentation scale W frag . We conjecture that the fragmentation identified here provides a geometric mechanism contributing to the finite-time slowing down of relaxation observed in studies of disordered interacting systems.

Source: Physical Review Research

DOI: 10.1103/hvqr-6n3b

Authors: Ishita Modak, Rajesh Narayanan, Ferdinand Evers, Soumya Bera

Institutions: Indian Institute of Technology Bombay, Indian Institute of Technology Madras, University of Regensburg

Language: English

Topic: Quantum many-body systems

Subfield: Atomic and Molecular Physics, and Optics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $2,625