arXiv subjects

Hanen Hamdi

Publications and source records attributed to Hanen Hamdi.

5 recordsLinked to original sources

arXiv2023

Interlayer vibrational hybrid normal mode enabling molecular chiral phonons

Organic/inorganic interfaces formed by monolayer substrates and conjugated molecular adsorbates are attractive material platforms leveraging the modularity of organic compounds together with the long-range phenomena typical of condensed matter. New quantum states are known to be generated by electronic interactions in these systems as well as by their coupling with light. However, little is still known about hybrid vibrational modes. In this work, we discover from first principles the existence of an infrared-active chiral phonon mode in a pyrene-decorated MoSe$_{2}$ monolayer given by the combination of a frustrated rotation of the molecule around its central axis and an optical mode in the substrate. Our results suggest the possibility to enable phonon chirality in molecular superlattices.

cond-mat.mtrl-sci↗

arXiv2020

Stone-Wales defects in hexagonal boron nitride as ultraviolet emitters

Many quantum emitters have been measured close or near the grain boundaries of the two-dimensional hexagonal boron nitride where various Stone-Wales defects appear. We show by means of first principles density functional theory calculations that the pentagon-heptagon Stone-Wales defect is an ultraviolet emitter and its optical properties closely follow the characteristics of a 4.08-eV quantum emitter often observed in polycrystalline hexagonal boron nitride. We also show that the square-octagon Stone-Wales line defects are optically active in the ultraviolet region with varying gaps depending on their density in hexagonal boron nitride. Our results may introduce a paradigm shift in the identification of fluorescent centres in this material.

cond-mat.mtrl-sci↗

arXiv2019

Ab initio theory of negatively charged boron vacancy qubit in hBN

Highly correlated orbitals coupled with phonons in two-dimension are identified for paramagnetic and optically active boron vacancy in hexagonal boron nitride by first principles methods which are responsible for recently observed optically detected magnetic resonance signal. We report ab initio analysis of the correlated electronic structure of this center by density matrix renormalization group and Kohn-Sham density functional theory methods. By establishing the nature of the bright and dark states as well as the position of the energy levels, we provide a complete description of the magneto-optical properties and corresponding radiative and non-radiative routes which are responsible for the optical spin polarization and spin dependent luminescence of the defect. Our findings pave the way toward advancing the identification and characterization of room temperature quantum bits in two-dimensional solids.

cond-mat.mes-hall↗

arXiv2018

A Polar large polaron in WO3

This version withdrawn by arXiv administrators because the author did not have the right to agree to our license at the time of submission

cond-mat.mtrl-sci↗

arXiv2016

First-principles re-investigation of bulk WO3

Using first-principles calculations, we analyze the structural properties of tungsten trioxide WO3 . Our calculations rely on density functional theory and the use of the B1-WC hybrid functional, which provides very good agreement with experimental data. The hypothetical high-symmetry cubic reference structure combines several ferroelectric and antiferrodistortive (antipolar cation motions, rotations and tilts of oxygen octahedra) structural instabilities. The instability related to antipolar W motions combines with those associated to oxygen rotations and tilts to produce the biggest energy reduction, yielding a P21/c ground state. This non-polar P21/c phase is only different from the experimentally reported Pc ground state by the absence of a very tiny additional ferroelectric distortion. The calculations performed on a stoichiometric compound so suggest that the low temperature phase of WO3 is not intrinsically ferroelectric and that the reported ferroelectric character might arise from extrinsic defects such as oxygen vacancies. Independently, we also identify never observed R3m and R3c ferroelectric phases with large polarizations and low energies close to the P 21/c ground state, which makes WO3 a potential antiferroelectric material. The relative stability of various phases is discussed in terms of the couplings between different structural distortions, highlighting a very complex interplay involving improper-like couplings up to fourth order in the energy expansion in the cubic phase.

cond-mat.mtrl-sci↗