  Glasses have the interesting feature of being neither integrable nor fully
chaotic. They thermalize quickly within a subspace but thermalize much more
slowly across the full space due to high free energy barriers which partition
the configuration space into sectors. Past works have examined the
Rosenzweig-Porter (RP) model as a minimal quantum model which transitions from
localized to chaotic behavior. In this work we generalize the RP model in such
a way that it becomes a minimal model which transitions from glassy to chaotic
behavior, which we term the "Block Rosenzweig-Porter" (BRP) model. We calculate
the spectral form factors of both models at all timescales. Whereas the RP
model exhibits a crossover from localized to ergodic behavior at the Thouless
timescale, the new BRP model instead crosses over from glassy to fully chaotic
behavior, as seen by a change in the slope of the ramp of the spectral form
factor.
