Lecture

Moiré Flatland: Graphene and Twisted Bilayer Graphene

Graph Chat

Chat with Graph Search

Ask any question about EPFL courses, lectures, exercises, research, news, etc. or try the example questions below.

DISCLAIMER: The Graph Chatbot is not programmed to provide explicit or categorical answers to your questions. Rather, it transforms your questions into API requests that are distributed across the various IT services officially administered by EPFL. Its purpose is solely to collect and recommend relevant references to content that you can explore to help you answer your questions.

Description

This lecture by the instructor covers the discovery and properties of graphene, including its one-atom thickness and hexagonal lattice structure. It delves into twisted bilayer graphene, explaining the concept of Moiré superlattice and the magic angle phenomenon, leading to unconventional superconductivity and different phases observed in twisted bilayer graphene.

Official source

Ontological neighbourhood

Physics

Condensed matter physics: Phase transitions

Related concepts (32)

Graphene

Graphene (ˈgræfiːn) is an allotrope of carbon consisting of a single layer of atoms arranged in a hexagonal lattice nanostructure. The name is derived from "graphite" and the suffix -ene, reflecting the fact that the graphite allotrope of carbon contains numerous double bonds. Each atom in a graphene sheet is connected to its three nearest neighbors by σ-bonds and a delocalised π-bond, which contributes to a valence band that extends over the whole sheet.

Bilayer graphene

Bilayer graphene is a material consisting of two layers of graphene. One of the first reports of bilayer graphene was in the seminal 2004 Science paper by Geim and colleagues, in which they described devices "which contained just one, two, or three atomic layers" Bilayer graphene can exist in the AB, or Bernal-stacked form, where half of the atoms lie directly over the center of a hexagon in the lower graphene sheet, and half of the atoms lie over an atom, or, less commonly, in the AA form, in which the layers are exactly aligned.

Twistronics

Twistronics (from twist and electronics) is the study of how the angle (the twist) between layers of two-dimensional materials can change their electrical properties. Materials such as bilayer graphene have been shown to have vastly different electronic behavior, ranging from non-conductive to superconductive, that depends sensitively on the angle between the layers. The term was first introduced by the research group of Efthimios Kaxiras at Harvard University in their theoretical treatment of graphene superlattices.

Superconductivity

Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered, even down to near absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero.

Electronic band structure

In solid-state physics, the electronic band structure (or simply band structure) of a solid describes the range of energy levels that electrons may have within it, as well as the ranges of energy that they may not have (called band gaps or forbidden bands). Band theory derives these bands and band gaps by examining the allowed quantum mechanical wave functions for an electron in a large, periodic lattice of atoms or molecules.

Related lectures (64)

Graphene: Quantum Properties and Nanoribbons

Explores graphene's quantum conductance, special electronic properties, nanoribbon fabrication, and edge effects.

Electron Localization in Incommensurately Stacked Layers of 2D Materials

Explores electron localization in incommensurately stacked 2D materials, including twisted bilayer graphene and transition metal di-chalcogenides.

Density Functional Theory and Tight-Binding Models

Explores modeling multilayer 2D materials, tight-binding models, and electrical conductivity in materials, emphasizing the importance of symmetries and reduced models.

Graphene Properties and Applications

Explores graphene properties, band structure, electronics, and nanoscale phenomena like the Quantum Hall effect and the Casimir effect.

Engineering Carbon Nanostructures