Antiscreening and Nonequilibrium Layer Electric Phases in Layered 2D Materials

When driven out of equilibrium, electronic systems can host a variety of internal fields (e.g., dc or ac electric fields or currents) which cannot be supported in equilibrium. Through electron-electron interactions, such fields may act back on the underlying electronic structure to reveal intriguing new dynamical phenomena or non-equilibrium phases of matter. In this talk I will describe our recent work demonstrating 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.