Tuning Material Properties: Insights Into Twisted Bilayer Graphene and Moire Materials Through Electronic Interactions
Jalen Harris, Cornell University
The field of two-dimensional (2-D) materials began with the discovery of monolayer graphene, isolated from bulk graphite. Since then, researchers have studied various 2-D crystals and predicted the existence of others, enabling the modification of material properties without changing their chemical makeup. Different methods, such as straining, atom removal, stacking of 2-D crystals, and electron manipulation, have been employed. Adjusting the relative orientation between 2-D crystals has been especially important since the discovery of twisted bilayer graphene.
Twisted bilayer graphene consists of two layers of graphene stacked with a relative twist angle (θ). At specific twist angles, a periodic pattern called the bilayer moire pattern emerges, resulting in narrow electronic minibands. Charge neutrality at these twist angles is less dispersed, and electron interactions play a significant role. Varying electron filling reveals insulating states at specific electron counts, and introducing charge carriers leads to properties like superconductivity.
In 2011, Bistritzer and Macdonald proposed a model to explain the electronic properties of twisted bilayer graphene, including the magic angles where the Fermi velocity approaches zero, enhancing electronic interactions. Experimental observations confirmed Mott insulation and superconductivity at the first and largest magic angle (θ = 1). Further discoveries of moire materials with superconductivity and correlated electronic phases followed. The validity of the Bistritzer-Macdonald-based moire models is essential to assess comprehensively.
This poster presents ongoing research on interacting Bistritzer-Macdonald models, specifically exploring their behavior under different settings, such as the influence of magnetic fields and beyond Hartree-Fock electronic correlation effects. We aim to deepen our understanding of these materials and their unique electronic properties, contributing to potential applications in this exciting field.
Abstract Author(s): Jalen Harris