  Screening is a ubiquitous phenomenon through which the polarization of bound
or mobile charges tends to reduce the strengths of electric fields inside
materials. Here we show how photoexcitation can be used as a knob to transform
conventional out-of-plane screening into anti-screening - the amplification of
electric fields - in multilayer graphene stacks. We find that, by varying the
photoexcitation intensity, multiple nonequilibrium screening regimes can be
accessed, including near-zero screening, anti-screening, or overscreening
(reversing electric fields). Strikingly, at modest continuous wave
photoexcitation intensities, the nonequilibrium polarization states become
multistable, hosting light-induced ferroelectric-like steady states with
nonvanishing out-of-plane polarization (and band gaps) even in the absence of
an externally applied displacement field in nominally inversion symmetric
stacks. This rich phenomenology reveals a novel paradigm of dynamical quantum
matter that we expect will enable a variety of nonequilibrium broken symmetry
phases.
