UG Seminar with Bryan Li on Perturbation Theory

This is a mathematical physics talk, but requires little in terms of math background. The existence of Dirac cones in twisted bilayer graphene was mathematically proved by Yang and Tao in 2023. I will walk through its proof. The main ingredient is converting the problem of finding eigenvalues of an infinite-dimensional operator to the computation of the determinant of a 2x2 matrix.