First-Principles Theory and Insights of 2D Ferroelectric Semiconductors and Semimetals

Nanoscale ferroelectrics hold promises for many miniaturized devices. Here we present first-principles prediction and understanding of three 2D ferroelectrics, including (a) semiconducting 2D group IV monochalcogenides [1], (b) semiconducting 2D multiferroic semiconductors in monolayer transition metal phosphorus chalcogenides (TMPCs) with coexisting ferroelectricity and ferromagnetism [2], and (c) semimetallic few-layer WTe₂ [3,4]. Monolayer group IV monochalcogenides hold anisotropic and large ferroelectric polarization with visible-spectrum excitonic gap, sizable exciton binding energy and strain-tunable ferroelectric transition barrier. In contrast, monolayer TMPCs hold coexisting ferroelectricity and ferromagnetism with out-of-plane electric polarization, suggesting the possibility of controlling polarization by external electric field. Finally, we show that ferroelectric polarization in few-layer WTe₂ is originated from interlayer sliding, enabling facile ferroelectric switching upon electric gating demonstrated in experiment very recently [4]. References: [1] 2D Materials 4, 015042 (2017). [2] APL 113, 043102 (2018). [3] npj Comput. Mater. 5, 119 (2019). [4] Nat. Phys. 16, 1028-1034 (2020).