PhySU Colloquium - Correlated Topological Phases in Two-Dimensional Materials

The PhySU Undergraduate Colloquia are weekly presentations given by undergraduate students on physics topics, intended to make a wider variety of subject areas more accessible to the student body.
This week, Sam Paudel is presenting “Correlated Topological Phases in Two-Dimensional Materials”. In solid-state physics, a material’s electronic structure is shaped by the atomic arrangement of atoms in a periodic array known as a lattice, influencing properties such as its conductivity. Often times, we can understand the behavior of electrons through their energy-momentum relationship, also known as the electronic band structure. This formalism helps explain unintuitive phenomena like forbidden energy states in the solid and electrons with seemingly lower masses.
However, it turns out that the single-electron band picture breaks down as the interactions between electrons intensify. Graphene, a single layer of carbon atoms in a hexagonal lattice, is a two-dimensional material which offers the ability to directly tune electronic bands in a lab and study the effects on electron dynamics. By introducing a twist between layers of graphene, bands flatten at specific “magic angles”, effectively reducing the velocity of electrons as they move through the solid. This can result in a strange phase of matter where topologically protected currents can flow along the edge of the material, despite the bulk being an insulator. These states are collectively known as topological insulators. The phase evolution of electronic wavefunctions and topological invariants characterize these states and show how topological properties of electronic bands lead to distinct bulk and edge states in two-dimensional materials.
This presentation will cover the fundamentals of solid-state physics, discuss why the unique band structure of graphene makes it a particularly interesting system to study, and illustrate how strongly correlated electrons manifest as topological phases in two-dimensional materials.
To sign up to present a colloquium for the 2024 Fall term, please visit this link: forms.gle/pXF9...