Chapter 10 - Focus Topic I: Transition Metal Dichalcogenides Flashcards
1
Q
What is an exciton?
A
An exciton is a bound electron-hole pair.
2
Q
What two classes of excitons exist? How are they described?
A
Free excitons, that are delocalized over many lattice sites. Described with effective mass model.
Bound excitons, highly localized in single unit cell. Needs to be described within framework of the full bandstructure.
3
Q
How do we describe excitons that extend over many crystal unit cells?
A
We use the effective mass theory. We start with a 2-particle Schrödinger equation. This is transformed to a center of mass reference frame. The Hamiltonian is now split into “centre of mass motion of e-h pair” and “internal e-h motion” parts. The size of the exciton is then determined by the hydrogenic 1s-wavefunction.
