Fig. 4: Page curves and entanglement spectrum.

a Entanglement entropy as a function of the subsystem size N_A on a periodic nine-plaquette chain in the zero-momentum and reflection symmetric sector with \({j}_{\max }=1\). The states are labeled and colored by their energies relative to the ground state energy ΔE = E − E₀ in lattice units. b Comparison of entanglement entropy (blue dots) and associated thermal entropy (red dashed line) of all eigenstates of the periodic nine-plaquette chain with \({j}_{\max }=1\) and ag² = 1.2 in a subsystem of length N_A = 4. The green vertical line indicates β = 0 and everything on its left (β > 0) is part of the physical spectrum.