  A wide range of disordered materials, including disordered correlated
systems, show "Universal Dielectric Response" (UDR), followed by a superlinear
power-law increase in their optical responses over exceptionally broad
frequency regimes. While extensively used in various contexts over the years,
the microscopics underpinning UDR remains controversial. Here, we investigate
the optical response of the simplest model of correlated fermions,
Falicov-Kimball model (FKM), across the continuous metal-insulator transition
(MIT) and analyze the associated quantum criticality in detail using cluster
extension of dynamical mean field theory (CDMFT). Surprisingly, we find that
UDR naturally emerges in the quantum critical region associated with the
continuous MIT. We tie the emergence of these novel features to a many-body
orthogonality catastrophe accompanying the onset of strongly correlated
electronic glassy dynamics close to the MIT, providing a microscopic
realization of Jonscher's time-honored proposal as well as a rationale for
similarities in optical responses between correlated electronic matter and
canonical glass formers.
