2 research outputs found
Exciton Relaxation Cascade in Two-dimensional Transition-metal dichalcogenides
Monolayers of transition-metal dichalcogenides (TMDs) are characterized by an
extraordinarily strong Coulomb interaction giving rise to tightly bound
excitons with binding energies of hundreds of meV. Excitons dominate the
optical response as well as the ultrafast dynamics in TMDs. As a result, a
microscopic understanding of exciton dynamics is the key for technological
application of these materials. In spite of this immense importance, elementary
processes guiding the formation and relaxation of excitons after optical
excitation of an electron-hole plasma has remained unexplored to a large
extent. Here, we provide a fully quantum mechanical description of momentum-
and energy-resolved exciton dynamics in monolayer molybdenum diselenide
(MoSe) including optical excitation, formation of excitons, radiative
recombination as well as phonon-induced cascade-like relaxation down to the
excitonic ground state. Based on the gained insights, we reveal experimentally
measurable features in pump-probe spectra providing evidence for the exciton
relaxation cascade
Molecule signatures in photoluminescence spectra of transition metal dichalcogenides
Monolayer transition metal dichalcogenides (TMDs) show an optimal
surface-to-volume ratio and are thus promising candidates for novel molecule
sensor devices. It was recently predicted that a certain class of molecules
exhibiting a large dipole moment can be detected through the activation of
optically inaccessible (dark) excitonic states in absorption spectra of
tungsten-based TMDs. In this work, we investigate the molecule signatures in
photoluminescence spectra in dependence of a number of different experimentally
accessible quantities, such as excitation density, temperature as well as
molecular characteristics including the dipole moment and its orientation,
molecule-TMD distance, molecular coverage and distribution. We show that under
certain optimal conditions, even room temperature detection of molecules can be
achieved