Kavli Affiliate: Jeffrey B. Neaton
| First 5 Authors: Marina R. Filip, Jonah B. Haber, Jeffrey B. Neaton, ,
| Summary:
The ab initio Bethe-Salpeter equation (BSE) approach, an established method
for the study of excitons in materials, is typically solved in a limit where
only static screening from electrons is captured. Here, we generalize this
framework to also include dynamical screening from phonons at lowest order in
the electron-phonon interaction. We apply this generalized BSE approach to a
series of inorganic lead halide perovskites, CsPbX3, with X = Cl, Br, and I. We
find that inclusion of screening from phonons significantly reduces the
computed exciton binding energies of these systems. By deriving a simple
expression for phonon screening effects, we reveal general trends for the
importance of phonon screening effects in semiconductors and insulators, based
on a hydrogenic exciton model. We demonstrate that the magnitude of the phonon
screening correction in isotropic materials can be reliably predicted using
four material specific parameters: the reduced effective mass, the static and
optical dielectric constants, and the phonon frequency of the most strongly
coupled LO phonon mode. This framework helps to elucidate the importance of
phonon screening and its relation to excitonic properties in a broad class of
semiconductors.
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