Timothy Berkelbach

3:15 p.m. – Public research seminar, Taylor Auditorium
4:30 p.m. – Research proposal, A81

Microscopic theories of excitons in emerging materials

Strongly bound excitons are ubiquitous in nanoscale materials and require a theoretical description which is intermediate between single molecules and conventional bulk semiconductors. In the first part of my talk, I will present recent work on excitons in organic molecular crystals.  In particular, I will present a dynamical theory of singlet fission, a process whereby a photoexcited spin singlet exciton decays into two spin triplet excitons.  This form of multiple exciton generation can be exploited to produce inexpensive solar cells with high efficiencies.  In the second part of my talk, I will discuss an ongoing research agenda to understand the diverse many-body phenomena exhibited by monolayer transition metal dichalcogenides such as molybdenum disulfide.  I will describe a microscopic effective-mass theory employing model dielectric functions which has been used to understand the spectroscopy of excitons, charged excitons (trions), and bi-excitons.  Extensions to realistic samples that include structural defects and carrier doping will also be presented.  Potential device applications of these materials due to their unusually strong interactions will be discussed throughout.