Fock space fragmentation in quenches of disordered interacting fermions

Hilbert 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 non-ergodic 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 (MBL). Specifically, we split 
the Fock-space into subspaces, potential-energy shells, which contain 
the accessible phase space for the relaxation of a quenched initial 
state.