A scalable network model for electrically tunable ferroelectric domain structure in twistronic bilayers of two-dimensional semiconductors

Abstract

Moiré structures in small-angle-twisted bilayers of two-dimensional (2D) semiconductors with a broken-symmetry interface form arrays of ferroelectric (FE) domains with periodically alternating out-of-plane polarization. Here, we propose a network theory for the tunability of such FE domain structure by applying an electric field perpendicular to the 2D crystal. Using multiscale analysis, we derive a fully parametrized string-theory-like description of the domain wall network (DWN) and show that it undergoes a qualitative change, after the arcs of partial dislocation (PD) like domain walls merge (near the network nodes) into streaks of perfect screw dislocations (PSD), which happens at a threshold displacement field dependent on the DWN period.

Theory of polar domains in moiré heterostructures

“…Applying this concept to a twisted bilayer, the stacking domains can be considered polar domains, where neighboring domains have opposite polarization. It has been suggested that the relative sizes of these domains can be tuned with the application of an electric field perpendicular to the bilayer, leading to a nonzero total polarization of the superlattice [10,11], which can be very nonlinear when the moiré period is large. Although experimental * db729@cantab.ac.uk measurements clearly show a ferroelectric response in homobilayers, from a theoretical perspective an ideal homo-bilayer has zero total polarization at zero field [10].…”

“…Separate to the question of whether or not the overall system exhibits a ferroelectric response is the question of whether or not the stacking domains themselves are ferroelectric. Several theoretical studies have claimed, without any justification, that the stacking domains in homo-bilayers are ferroelectric [11][12][13]. This is simply incorrect: the domains are determined by the structure, and even if they change in area in response to an applied field, the orientation of the polarization in each domain is pinned cannot be inverted [10].…”