Exchangeable Hoeffding decompositions over finite sets: a characterization and counterexamples

in Journal of Multivariate Analysis (2014), 131

Excitation energy and pair correlation function of trions near an LiF surface

in Physical Review B (2008), 78(15),

We investigate the excitation spectrum of a singly charged LiF surface using an embedded cluster approach. The spectrum is determined by multiconfiguration self-consistent field calculations. We find ... [more ▼]

We investigate the excitation spectrum of a singly charged LiF surface using an embedded cluster approach. The spectrum is determined by multiconfiguration self-consistent field calculations. We find stable trionic states, i.e., quasimolecular states of a three-quasiparticle complex consisting of two holes and one electron interacting through the Coulomb potential. The excitation energy of the lowest trionic state is approximately 12.1 eV. The mean hole-hole spacing is about 7.6 a.u. (or 4 A). Our results confirm the interpretation of experiments [P. Roncin , Phys. Rev. Lett. 89, 043201 (2002)] where trion excitation was suggested as effective energy-loss channel during the neutralization of Ne(+) ions at an LiF surface. [less ▲]

Exciton-Phonon Coupling in the Ultraviolet Absorption and Emission Spectra of Bulk Hexagonal Boron Nitride

in PHYSICAL REVIEW LETTERS (2019), 122(18), 187401-6

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 ... [more ▼]

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. [less ▲]

Excitons in a mirror: Formation of “optical bilayers” using MoS2 monolayers on gold substrates

in Applied Physics Letters (2014), 104

We report coupling of excitons in monolayers of molybdenum disulphide to their mirror image in an underlying gold substrate. Excitons at the direct band gap are little affected by the substrate whereas ... [more ▼]

We report coupling of excitons in monolayers of molybdenum disulphide to their mirror image in an underlying gold substrate. Excitons at the direct band gap are little affected by the substrate whereas strongly bound C-excitons associated with a van-Hove singularity change drastically. On quartz substrates only one C-exciton is visible (in the blue) but on gold substrates a strong red-shifted extra resonance in the green is seen. Exciton coupling to its image leads to formation of a “mirror biexciton” with enhanced binding energy. Estimates of this energy shift in an emitter-gold system match experiments well. The absorption spectrum of MoS2 on gold thus resembles a bilayer of MoS2 which has been created by optical coupling. Additional top-mirrors produce an “optical bulk.” [less ▲]

Excitons in boron nitride single layer

in Physical Review. B : Condensed Matter (2016), 94(125303),

Boron nitride single layer belongs to the family of two-dimensional materials whose optical properties are currently receiving considerable attention. Strong excitonic effects have already been observed ... [more ▼]

Boron nitride single layer belongs to the family of two-dimensional materials whose optical properties are currently receiving considerable attention. Strong excitonic effects have already been observed in the bulk and still stronger effects are predicted for single layers. We present here a detailed study of these properties by combining ab initio calculations and a tight-binding Wannier analysis in both real and reciprocal space. Due to the simplicity of the band structure with single valence (π) and conduction (π∗) bands the tight-binding analysis becomes quasiquantitative with only two adjustable parameters and provides tools for a detailed analysis of the exciton properties. Strong deviations from the usual hydrogenic model are evidenced. The ground-state exciton is not a genuine Frenkel exciton, but a very localized tightly bound one. The other ones are similar to those found in transition-metal dichalcogenides and, although more localized, can be described within a Wannier-Mott scheme. [less ▲]

Excitons in transition metal dichalcogenides. A theoretical approach

Scientific Conference (2013)

Excludability: A laboratory study on forced ranking in team production

in Journal of Economic Behavior & Organization (2015), 114

Exclusion of the C/D box snoRNA gene cluster HBII-52 from a major role in Prader–Willi syndrome

in Human Genetics (2005), 116(3), 228-230

Executing Trades in Style: Retail Investors vs. Institutions

E-print/Working paper (2018)

Exécution des contrats et exécution des décisions de justice

in L'exécution (1999)