Validity of generalized Gibbs ensemble in a random matrix model with a global $\mathbb{Z}_2$-symmetry

Abstract: $\mathbb{Z}_2$ symmetry is ubiquitous in quantum mechanical systems where it drives various phase transitions and emergent physics. To understand the role of $\mathbb{Z}_2$ symmetry in the thermalization of a local observable in a disordered system, we consider random symmetric centrosymmetric (SC) matrices where the exchange symmetry is conserved. Such a conservation law splits the Hilbert space into decoupled subspaces such that the energy spectrum of a SC matrix is a superposition of two pure spectra. After discussing the known results on the correlations of such mixed spectrum, we consider different initial states and analytically compute the entire time evolution of their survival probability and associated timescales. We show that there exist certain initial states which do not decay over a very long timescales such that a measure zero fraction of random SC matrices exhibit spontaneous symmetry breaking. Later, we show that thermalization is violated for a generic local observable in case of the SC matrices, where the generalized Gibbs ensemble accurately captures the equilibrium expectation values.