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Overtones of interlayer shear modes in the phonon-assisted emission spectrum of hexagonal boron nitride 
Auteur(s): Vuong P., Cassabois G. , Valvin P., Jacques V., Cusco R., Artus L., Gil B.
(Article) Publié:
Physical Review B, vol. 95 p.045207 (2017)
Texte intégral en Openaccess : 
Ref HAL: hal-01475800_v1
DOI: 10.1103/PhysRevB.95.045207
WoS: WOS:000392074700012
Exporter : BibTex | endNote
16 Citations
Résumé: We address the intrinsic optical properties of hexagonal boron nitride in the deep ultraviolet. Weshow that the fine structure of the phonon replicas arises from overtones involving up to six low-energy interlayer shear modes. These lattice vibrations are specific to layered compounds since theycorrespond to the shear rigid motion between adjacent layers, with a characteristic energy of about6-7 meV. We obtain a quantitative interpretation of the multiplet observed in each phonon replicaunder the assumption of a cumulative Gaussian broadening as a function of the overtone index,and with a phenomenological line-broadening taken identical for all phonon types. We show fromour quantitative interpretation of the full emission spectrum above 5.7 eV that the energy of theinvolved phonon mode is 6.8±0.5 meV, in excellent agreement with temperature-dependent Ramanmeasurements of the low-energy interlayer shear mode in hexagonal boron nitride. We highlightthe unusual properties of this material where the optical response is tailored by the phonon groupvelocities in the middle of the Brillouin zone.
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Phonon symmetries in hexagonal boron nitride probed by incoherent light emission
Auteur(s): Vuong P., Cassabois G., Valvin P., Jacques V., van Der Lee Arie, Zobelli Alberto, Watanabe Kanji, Taniguchi Takashi, Gil B.
(Article) Publié:
2D Materials, vol. 4 p.011004 (2016)
Texte intégral en Openaccess :
Ref HAL: hal-01394786_v1
DOI: 10.1088/2053-1583/4/1/011004
WoS: 000388511000001
Exporter : BibTex | endNote
16 Citations
Résumé: Layered compounds are stacks of weakly bound two-dimensional atomic crystals, with a prototypal hexagonal structure in graphene, transition metal dichalcogenides and boron nitride. This crystalline anisotropy results in vibrational modes with specific symmetries depending on the in-plane or out-of- plane atomic displacements. We show that polarization-resolved photoluminescence measurements in hexagonal boron nitride reflect the phonon symmetries in this layered semiconductor. Experiments performed with a detection on the sample edge, perpendicular to the c-axis, reveal the strong polarization-dependence of the emission lines corresponding to the recombination assisted by the three acoustic phonon modes. We elucidate the dipole orientation of the fundamental indirect exciton. We demonstrate evidence of the so-far missing phonon replica due to the optical out-of- plane phonon mode.
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Phonon-Photon Mapping in a Color Center in Hexagonal Boron Nitride
Auteur(s): Vuong P., Cassabois G., Valvin P., Ouerghi Abdelkarim, Chassagneux Yannick, Voisin Christophe, Gil B.
(Article) Publié:
Physical Review Letters, vol. 117 p.097402 (2016)
Ref HAL: hal-01362938_v1
DOI: 10.1103/PhysRevLett.117.097402
WoS: 000382008400011
Exporter : BibTex | endNote
30 Citations
Résumé: We report on the ultraviolet optical response of a color center in hexagonal boron nitride. We demonstrate a mapping between the vibronic spectrum of the color center and the phonon dispersion in hexagonal boron nitride, with a striking suppression of the phonon assisted emission signal at the energy of the phonon gap. By means of nonperturbative calculations of the electron-phonon interaction in a strongly anisotropic phonon dispersion, we reach a quantitative interpretation of the acoustic phonon sidebands from cryogenic temperatures up to room temperature. Our analysis provides an original method for estimating the spatial extension of the electronic wave function in a point defect.
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