Twist-Controlled Ferroelectricity and Emergent Multiferroicity in WSe<sub>2</sub> Bilayers.

Hassan, Yasir; Singh, Budhi; Joe, Minwoong; Son, Byoung-Min; Ngo, Tien Dat; Jang, Younggeun; Sett, Shaili; Singha, Arup et al. · Adv Mater · 2024

basic_science · Level V

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Abstract

Recently, researchers have been investigating artificial ferroelectricity, which arises when inversion symmetry is broken in certain R-stacked, i.e., zero-degree twisted, van der Waals (vdW) bilayers. Here, the study reports the twist-controlled ferroelectricity in tungsten diselenide (WSe<sub>2</sub>) bilayers. The findings show noticeable room temperature ferroelectricity that decreases with twist angle within the range 0° < θ < 3°, and disappears completely for θ ≥ 4°. This variation aligns with moiré length scale-controlled ferroelectric dynamics (0° < θ < 3°), while loss beyond 4° may relate to twist-controlled commensurate to non-commensurate transitions. This twist-controlled ferroelectricity serves as a spectroscopic tool for detecting transitions between commensurate and incommensurate moiré patterns. At 5.5 K, 3° twisted WSe<sub>2</sub> exhibits ferroelectric and correlation-driven ferromagnetic ordering, indicating twist-controlled multiferroic behavior. The study offers insights into twist-controlled coexisting ferro-ordering and serves as valuable spectroscopic tools.