Superconductivity in twisted bilayer WSe₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Moiré materials exhibit flat electron bands, leading to strong electron correlations and quantum phases.
• Superconductivity was previously only observed in graphene-based moiré materials, leaving its absence in other systems like semiconductor moiré materials unexplained.
• This gap challenged the understanding of superconductivity within flat bands.

Purpose of the Study:

• To investigate the possibility of robust superconductivity in semiconductor moiré materials beyond graphene.
• To explore the underlying mechanisms of superconductivity in flat band systems.
• To understand the relationship between superconductivity, electron correlations, and charge localization.

Main Methods:

• Fabrication and characterization of twisted bilayer tungsten diselenide (WSe2) with specific twist angles (3.5° and 3.65°).
• Measurement of superconducting properties, including transition temperature and its relation to Fermi temperature.
• Tuning of external displacement fields to observe transitions between metallic, superconducting, and correlated insulating states.

Main Results:

• Robust superconductivity was observed in both 3.5° and 3.65° twisted bilayer WSe2.
• Superconductivity emerged near half-band filling and zero external displacement fields, with optimal transition temperatures around 200 mK.
• The superconducting state was found to border distinct metallic phases and transition continuously into a correlated insulator under varying displacement fields.

Conclusions:

• The discovery of superconductivity in WSe2 moiré materials expands the family of superconducting moiré systems.
• The observed superconductivity, occurring near charge localization, strongly suggests its origins in electron correlations.
• This work provides critical insights into the nature of superconductivity in strongly correlated flat band systems.