Untying the insulating and superconducting orders in magic-angle graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Magic-angle twisted bilayer graphene exhibits coexisting superconducting and correlated insulating states.
• Understanding the relationship between these phases is crucial for condensed matter physics.
• Independent control over their governing mechanisms is needed to elucidate their interplay.

Purpose of the Study:

• To directly tune electronic interactions in twisted bilayer graphene.
• To investigate the relationship between superconducting and correlated insulating states.
• To probe the microscopic mechanisms of superconductivity in strongly correlated systems.

Main Methods:

• Modulating the separation distance between graphene and a metallic screening layer.
• Fabricating devices with varying twist angles and screening layer separations.
• Applying small out-of-plane magnetic fields.

Main Results:

• Correlated insulators were quenched when screening layer separation was reduced below the typical 15 nm Wannier orbital size.
• Superconducting domes emerged in the phase space vacated by insulators, with comparable critical temperatures.
• Insulators at half-filling reappeared in a 0.4 T magnetic field, forming quantized Hall states with a Chern number of 2.

Conclusions:

• The study challenges the 'parent-and-child' relationship assumption between insulating and superconducting phases in moiré graphene.
• Direct tuning of electronic interactions provides a method to probe superconductivity mechanisms in strongly correlated systems.
• The findings offer new avenues for understanding complex quantum phenomena in twisted bilayer graphene.