Twist-Controlled Ferroelectricity and Emergent Multiferroicity in WSe₂ Bilayers

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Artificial ferroelectricity emerges in stacked van der Waals (vdW) bilayers with broken inversion symmetry.
• R-stacked, zero-degree twisted vdW bilayers are key to investigating this phenomenon.

Purpose of the Study:

• To investigate twist-controlled ferroelectricity in tungsten diselenide (WSe2) bilayers.
• To explore the relationship between twist angle and ferroelectric properties.
• To utilize twist-controlled ferroelectricity as a spectroscopic tool.

Main Methods:

• Fabrication of twisted WSe2 bilayers.
• Measurement of ferroelectric properties as a function of twist angle (0° < θ < 3°).
• Analysis of transitions between commensurate and incommensurate moiré patterns.

Main Results:

• Room temperature ferroelectricity observed, decreasing with twist angle (0° < θ < 3°) and disappearing at θ ≥ 4°.
• Ferroelectric dynamics linked to moiré length scale.
• Twist-controlled ferroelectricity identified as a tool for detecting moiré pattern transitions.
• Multiferroic behavior observed in 3° twisted WSe2 at 5.5 K, showing coexisting ferroelectric and ferromagnetic ordering.

Conclusions:

• Twist angle is a critical parameter for controlling ferroelectricity in WSe2 bilayers.
• Twist-controlled ferroelectricity provides insights into moiré pattern physics and multiferroic phenomena.
• This work establishes WSe2 bilayers as a promising platform for exploring tunable electronic and magnetic properties.