A tunable bilayer Hubbard model in twisted WSe₂.

Area of Science:

• Condensed Matter Physics
• Quantum Materials
• Materials Science

Background:

• Moiré materials with flat electronic bands offer tunable quantum systems for exploring strong-correlation physics and topology.
• Heterobilayers of transition metal dichalcogenides can model the single-band Hubbard model.
• Introducing layer degrees of freedom is key to richer interactions like Hund's physics and superconductivity.

Purpose of the Study:

• Investigate competing electronic states in twisted AB-homobilayer WSe2.
• Realize and study the bilayer Hubbard model in a solid-state system.
• Explore the effects of layer-polarizing holes using electric fields.

Main Methods:

• Fabrication of twisted AB-homobilayer WSe2.
• Application of perpendicular electric fields for layer-polarization of holes.
• Measurement of electronic states as a function of hole density (ν).

Main Results:

• Observed a crossover from excitonic to charge-transfer insulator at ν=1.
• Identified a transition from paramagnetic to antiferromagnetic charge-transfer insulator at ν=2.
• Found evidence for a layer-selective Mott insulator in the range 1 < ν < 2.
• Demonstrated a giant magnetoelectric response due to coupled charge and spin dynamics.

Conclusions:

• Twisted WSe2 realizes a bilayer Hubbard model in the weak interlayer hopping limit.
• The system exhibits diverse competing electronic and magnetic phases.
• This work provides a novel solid-state platform for simulating the bilayer Hubbard model and exploring complex quantum phenomena.