First demonstration of a system that allows gate-induced transitions between magnetic and superconducting phases in zero magnetic field

The discovery of magic angle twisted bilayer graphene (MATBG) has opened a whole new world for researchers to find and characterize new and exotic properties and states of this material like superconducting, magnetic and topological phases. However, the creation of induced gate transition between different phases (superconductor and correlated Chern insulator states) in zero magnetic field had remained difficult to achieve.

Now, an international team led by ICFO researchers Petr Stepanov, Xiaobo Lu and Dimitri Efetov, in collaboration with Ming Xie and Allan H. MacDonald from University of Texas at Austin (USA), Takashi Taniguchi and Kenji Watanabe from the National Institute of Material Sciences (Japan) and B. Andrei Bernevig from University of Princeton (USA), have conducted the first experimental demonstration of a device that is both a Chern insulator and a superconductor in a zero magnetic field.  They report these findings in a new paper recently published in the journal Physical Review Letters.

Chern insulators are topological insulators, which means that they are able to conduct electricity on their surface or edge but not in their bulk.

To carry out their study, the researchers built a four-terminal transport device. The device consisted of two sheets of graphene twisted together at an angle of 1,08º and encapsulated by two non-aligned layers of hexagonal boron nitride (hBN) and a base of graphite. They performed several transport and direct current measurements on this heterostructure at temperatures around 50mK, and found that the system behaved as an insulator and as a superconductor by gate induced transitions

According to the authors of the study, their “observations mark a major milestone in the creation of a new generation of quantum electronics”.

Original Study

Stepanov, P., Xie, M., Taniguchi, T., Watanabe, K., Lu, X., MacDonald, A. H., Bernevig, B. A., Efetov, D. K. (2021). Competing Zero-Field Chern Insulators in Superconducting Twisted Bilayer Graphene. Physical Review Letters, 127(19), 197701. https://doi.org/10.1103/PhysRevLett.127.197701