Untying the insulating and superconducting orders in magic-angle graphene

A TYC member at Imperial College London has worked with a team of international researchers to publish a study on 'Untying the insulating and superconducting orders in magic-angle graphene'. Johannes Lischner says that twisted bilayer graphene is one of the newest two-dimensional materials. It consists of two graphene sheets placed on top of each other and then rotated against each other. This rotation creates a moire pattern which leads to novel properties.

Twisted bilayer graphene is one of the latest additions to the ever expanding zoo of two-dimensional materials. 

It consists of two graphene sheets placed on top of each other and then rotated against each other. This rotation (or twist) creates a moire pattern which leads to novel properties. In particular, it was demonstrated that a rotation of 1.1 degrees (known as the magic angle) transforms the metallic material into an insulator. Upon cooling, magic-angle twisted bilayer graphene becomes a superconductor. This is reminiscent of the electronic phase diagram of the cuprates, the class of materials with the highest known superconducting transition temperatures. This outward similarity of twisted bilayer graphene and the cuprates led many researchers to believe that the underlying microscopic mechanisms that give rise to these phases are also similar. However, our new findings cast doubts on this assumption. 

In particular, we were able to demonstrate that the insulating phase and the superconducting phase are not strongly linked to each other: it is possible to destroy the insulator by bring a metal into the close vicinity of the twisted bilayer while maintaining the superconducting state. In contrast, the two phases are believed to be strongly linked in the cuprates with spin fluctations from the insulating antiferromagnetic parent state providing the glue that binds electrons into Cooper pairs.

Read the full article in Nature

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