ATM - Theoretical Basics of Optically Excited Excitons and Their Coupling to the Environment

Excitons lie at the heart of the optical and electronic properties of atomically thin layers. 

But what exactly is an exciton from a theoretical perspective? How do they emerge after optical excitation? And what is the difference between excitons in atomically thin semiconductors and molecular monolayers?

In this hands-on theoretical course, we will build up the physics of Wannier- and Frenkel-excitons step by step - starting from individual electronic excitations, and gradually moving towards collective excitonic states in two band semiconductors and molecular lattices. We will study which Coulomb interactions bind electrons and holes into excitons and how phonons induce optical dephasing, examining how this manifests in the optical response of a material.

You will work directly with the modern theoretical tools used to describe optically excited systems – including code writing. We will construct Hamiltonians, derive observables with the Heisenberg equation of motion and, by using the programming language Python, calculate properties of molecular excitons like binding energies and oscillator strengths. Finally, we will connect the microscopic exciton dynamics to macroscopic observables such as absorption and optical spectra by using Maxwell Theory. 

You will learn:

• How to use the formalism of Second Quantization and the Heisenberg equation of motion to study excitons in semiconducting and molecular crystals.
• How to derive optical observables by combining quantum theory with Electrodynamics.
• How to use Python to calculate binding energies, transition dipole moments and dephasing- / lifetimes of excitons.

Advanced Training Modules focus on specific theoretical and experimental techniques in the science of mol2Dmat heterostructures and form part of the iRTG curriculum. This ATM will be facilitated by Prof. Andreas Knorr and Michiel Snoeken from TU Berlin (CRC project A03), and will count as 1 credit point. 

Programme

Tuesday, 15 September 2026

• 09:00 Arrival
• 09:15 - 17:00 Theoretical introduction
• Breaks and a one-hour lunch break are included

Wednesday, 16 September 2026

• 09:00 Arrival
• 09:15 - 12:30 Coding with Python
• One break is included