Exciton-Phonon Coupling in the Ultraviolet Absorption and Emission Spectra of Bulk Hexagonal Boron Nitride
English
Paleari, Fulvio[University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit]
Miranda, Henrique P. C.[University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit > > > > ; Catholic Univ Louvain, Inst Condensed Matter & Nanosci, Chemin Etoiles 8,Bte L7-03-01, B-1348 Louvain La Neuve, Belgium]
[en] We present an ab initio method to calculate phonon-assisted absorption and emission spectra in the presence of strong excitonic effects. We apply the method to bulk hexagonal BN, which has an indirect band gap and is known for its strong luminescence in the UV range. We first analyze the excitons at the wave vector (q) over bar of the indirect gap. The coupling of these excitons with the various phonon modes at (q) over bar is expressed in terms of a product of the mean square displacement of the atoms and the second derivative of the optical response function with respect to atomic displacement along the phonon eigenvectors. The derivatives are calculated numerically with a finite difference scheme in a supercell commensurate with (q) over bar. We use detailed balance arguments to obtain the intensity ratio between emission and absorption processes. Our results explain recent luminescence experiments and reveal the exciton-phonon coupling channels responsible for the emission lines.
FNR, Luxembourg [EXCPHON/11280304, INTER/ANR/13/20/NANOTMD] ; Juan de la Cierva program (MINECO, Spain) [IJCI-2015-25799] ; F.R.S.-FNRS through the PDR Grants HTBaSE [T.1071.15]
F.P. and L.W. acknowledge support from the FNR, Luxembourg (Projects No. EXCPHON/11280304 and No. INTER/ANR/13/20/NANOTMD, respectively). A.M.-S. acknowledges the Juan de la Cierva (Grant No. IJCI-2015-25799) program (MINECO, Spain). H.P. C.M. acknowledges the F.R.S.-FNRS through the PDR Grants HTBaSE (T.1071.15). We acknowledge F. Giustino for suggesting the use of the RS relation and M. Zacharias, T. Galvani, M. Barborini, and S. Reichardt for stimulating discussions. We are also indebted to T.Q.P. Vuong, G. Cassabois, B. Gil, and J. Barjon for critical observations about the preliminary results.
FnR ; FNR11280304 > Fulvio Paleari > > Phonon-assisted optical absorption in layered materials > 01/04/2016 > 31/10/2019 > 2016; FNR7490149 > Ludger Wirtz > NANOTMD > 20 Electric transport and superconductivity in TransitionMetal Dichalcogenides nanolayers > 01/02/2014 > 31/01/2019 > 2013
[University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit]
