Correlated insulator behaviour at half-filling in magic-angle graphene superlattices

Van der Waals (vdW) heterostructures are an emergent class of metamaterials comprised of vertically stacked two-dimensional (2D) building blocks, which provide us with a vast tool set to engineer their properties on top of the already rich tunability of 2D materials. 1 One of the knobs, the twist angle between different layers, plays a crucial role in the ultimate electronic properties of a vdW heterostructure and does not have a direct analog in other systems such as MBE-grown semiconductor heterostructures. For small twist angles, the moiré pattern produced by the lattice misorientation creates a long-range modulation. So far, the study of the effect of twist angles in vdW heterostructures has been mostly concentrated in graphene/hex a gonal boron nitride (h-BN) twisted structures, which exhibit relatively weak interlayer interaction due to the presence of a large bandgap in h-BN. 2-5 Here we show that when two graphene sheets are twisted by an angle close to the theoretically predicted ‘magic angle’, the resulting flat band structure near charge neutrality gives rise to a strongly-correlated electronic system . 6 These flat bands exhibit half-filling insulating phases at zero magnetic field, which we show to be a Mott-like insulator arising from electrons localized in the moiré superlattice. These unique properties of magic-angle twisted bilayer graphene (TwBLG) open up a new playground for exotic many-body quantum phases in a 2D platform made of pure carbon and without mag netic field. The easy accessibility of the flat bands, the electrical tunability, and the bandwidth tunability though twist angle may pave the way towards more exotic correlated systems, such as unconventional superconductors or quantum spin liquids

Whether highly curious students thrive academically depends on perceptions about the school learning environment: A study of Hong Kong adolescents

The present study tested whether the perceived academic values of a school moderate whether highly curious students thrive academically. We investigated the interactive effects of curiosity and school quality on academic success for 484 Hong Kong high school students. Chinese versions of the Curiosity and Exploration Inventory, Subjective Happiness Scale, and Rosenberg Self-Esteem scales were administered and shown to have acceptable measurement properties. We obtained Hong Kong Certificate of Education Examination (HKCEE) scores (national achievement tests) from participating schools. Results yielded Trait Curiosity × Perceived School Quality interactions in predicting HKCEE scores and school grades. Adolescents with greater trait curiosity in more challenging schools had the greatest academic success; adolescents with greater trait curiosity in less challenging schools had the least academic success. Findings were not attributable to subjective happiness or self-esteem and alternative models involving these positive attributes were not supported. Results suggest that the benefits of curiosity are activated by student beliefs that the school environment supports their values about growth and learning; these benefits can be disabled by perceived person-environment mismatches. © 2007 Springer Science+Business Media, LLC.link_to_subscribed_fulltex