Equilibrium statistical physics holds true for an ergodic system which loses information of its initial condition by equally exploring all its accessible states under time evolution. In the last decade, a flurry of theoretical work has shown that ergodicity can be broken in an isolated, quantum many-body system even at high energies in the presence of disorder, a phenomena known as many-body localization (MBL).

In this talk I will discuss mean-field models for quantum spin glasses and their eigenstate properties. For strong transverse field the system is ergodic and satisfies the eigenstate thermalization hypothesis (ETH), while for weak fields the eigenstates below a critical energy violate ETH. The non-ergodic eigenstates at a finite energy density are organized in clusters with distinct magnetization patterns, reminiscent of the clustering transition in spin glass theory.