Superlubric sliding ferroelectricity

Structural superlubricity at incommensurate van der Waals interfaces leads to ultra-low friction coefficients. In this study, we try to apply a similar strategy to reduce the barrier of sliding ferroelectricity in van der Waals bilayers/multilayers with commensurate interfaces, since the writing speed in ferroelectric memories would be enhanced almost exponentially upon such reduction. A major challenge is that incommensurate interfaces are generally non-ferroelectric, and our solution is asymmetric across-layer stacking. We propose a type of superlubric sliding ferroelectricity in homobilayers separated by a hetero-layer, where the polarizations stem from symmetry breaking in across-layer commensurate stacking configurations. Meanwhile, the incommensurate interfaces of adjacent layers lead to unprecedented low switching barriers. For example, the switching barrier of 3R bilayer MoS2 will be, respectively, reduced by around two or one order of magnitudes (0.027 and 0.167 meV/atom) if they are separated by a graphene or BN monolayer, and the required voltage for switching can be about one order of magnitude lower. Such superlubric sliding ferroelectricity widely exists in various similar sandwich trilayer systems, where symmetry breaking induced by across-layer stacking configurations may also lead to considerable polarizations. With switching barriers three–four orders of magnitude lower compared with prevalent ferroelectrics, epochal applications, such as superlubric nanogenerators and picosecond ferroelectricity, may become feasible.