Room-temperature vertical ferroelectricity in rhenium diselenide induced by interlayer sliding

One variety of ferroelectricity that results from lateral relative movements between the adjacent atomic layers is referred to as sliding ferroelectricity,which generates an interfacial charge transfer and hence a polarization reversal.The mechanism of sliding ferroelectricity existent in van der Waals crystals is quite distinct from the conventional ferroelectric switching mechanisms mediated by ion displacement.It creates new possibilities for the design of two-dimensional(2D)ferroelectrics since it can be achieved even in non-polar systems.Before 2D ferroelectrics can be widely employed for practical implementations,however,there is still significant work to be done on several fronts,such as exploring ferroelectricity possibly in more potential 2D systems.Here,we report the experimental observation of room-temperature robust vertical ferroelectricity in layered semiconducting rhenium diselenide(ReSe_(2)),a representative member of the transition metal dichalcogenides material family,based on a combined research of nanoscale piezoresponse and second harmonic generation measurements.While no such ferroelectric behavior was seen in 1L ReSe_(2),2L ReSe_(2)exhibits vertical ferroelectricity at ambient environment.Based on density-functional theory calculations,we deduce that the microscopic origin of ferroelectricity for ReSe_(2)is uncompensated vertical charge transfer that is dependent on in-plane translation and switchable upon interlayer sliding.Our findings have important ramifications for the ongoing development of sliding ferroelectricity since the semiconducting properties and low switching barrier of ReSe2 open up the fascinating potential for functional nanoelectronics applications.

Electrically driven motion, destruction, and chirality change of polar vortices in oxide superlattices

Topological polar vortices, which are electric analogs of magnetic objects, present great potential in applications of future nanoelectronics because of their nanometer size, anomalous dielectric response, and chirality. To enable the functionalities, it is prerequisite to manipulate the polar states and chirality by using external stimuli. Here, we probe the evolutions of polar state and chirality evolutions of topological polar vortices in Pb TiO;/Sr TiO;superlattices under an electric field by using atomically resolved in situ scanning transmission electron microscopy and phase-field simulations. We find that, under electric field, the chiral vortex cores can be moved laterally to form close-pair structures, transform into a/c domain stripes, and finally become a nonchiral c-domain. Such transition is reversible and spontaneous after bias removal. Interestingly, during switching and backswitching events, the vortex rotation can be changed, offering a potential strategy to manipulate vortex chirality. The revealed dynamic behavior of individual polar vortices at the atomic scale provides fundamentals for future device applications.