arXiv subjects

Adlen Smiri

Publications and source records attributed to Adlen Smiri.

7 recordsLinked to original sources

arXiv2026

Alloy engineering of excitonic properties in TMD monolayers

We investigate monolayer MoS$_{2x}$Se$_{2(1-x)}$ alloys across the full composition range using optical spectroscopy. We demonstrate continuous tuning of the optical gap over $\sim$0.35 eV, accompanied by a systematic reduction of the B--A exciton splitting, in agreement with density functional theory calculations. Temperature-dependent measurements reveal a progressive increase of the average phonon energy from Se-rich to S-rich alloys that follows a simple reduced-mass scaling model. Polarization-resolved spectroscopy further shows a monotonic increase of the circular polarization from nearly zero in MoSe$_2$ to $\sim$15\% in MoS$_2$ at 78 K. The observed evolution of the polarization is attributed to alloy-induced modifications of the electronic structure that modify bright--dark exciton mixing and the associated valley depolarization. These findings establish alloy engineering as an effective strategy for controlling excitonic properties in TMD monolayers.

cond-mat.mtrl-sci↗

arXiv2026

Probing Dielectric Screening in van der Waals Heterostructures via Pressure-Tuned Exciton Rydberg Series

Excitons in two-dimensional semiconductors are directly exposed to the environment and are sensitive to the dielectric properties of their surrounding. Here, we show that the Rydberg series of excited states of excitons in a monolayer WSe$_2$ encapsulated in hexagonal boron nitride (hBN) can be used to probe the pressure-induced modifications of the surrounding dielectric properties. We propose a model based on the pressure induced evolution of the interlayer distances in this van der Waals heterostructure and on the bulk dielectric properties of hBN. This approach allows a direct measurement of the dielectric constant of pressurized hBN and establishes a new methodology for dielectric sensing.

cond-mat.mes-hall↗

arXiv2023

Layer-number and strain effects on the structural and electronic properties of PtSe2 material

Bandgap engineering of low-dimensional materials forms a robust basis for advancements in optoelectronic technologies. Platinum diselenide (PtSe2) material exhibits a transition from semi-metal to semiconductor (SM-SC) when going from bulk to monolayer (ML). In this work, density functional theory (DFT) with various van der Waals (vdW) corrections has been tested to study the effect of the layer-number on the structural and electronic properties of the PtSe2 material. The considered vdW corrections gave different results regarding the number of layers at which the SM-SC transition occurs. This variation is due to the different interlayer distances found for each correction, revealing the sensitivity of the bandgap to this distance in addition to the layer number. In fact, the bandgap increases with the increasing of the interlayer distance, due to the energy shift of conduction and valence bands dominated by Se-pz orbitals. According to the comparison with the available experimental data, the vdW corrections vdW-DF and rVV10 gave the most accurate results. Moreover, the control of the interlayer distance via vertical compressive strain led to the bandgap tuning of semiconductor PtSe2 BL. Indeed, a semi-metal character of PtSe2 BL can be obtained under 17% vertical strain. Our work shows a deep understanding of the correlation between the structural and electronic properties, and thus a possibility to tune the bandgap by strain means.

cond-mat.mtrl-sci↗

arXiv2020

Optical properties of exciton in two-dimensional transition metal dichalcogenide nanobubbles

Strain in two-dimensional (2D) transition metal dichalcogenide (TMD) has led to localized states with exciting optical properties, in particular in view of designing one photon sources. The naturally formed of the MoS2 monolayer deposed on hBN substrate leads to a reduction of the bandgap in the strained region creating a nanobubble. The photogenerated particles are thus confined in the strain-induced potential. Using numerical diagonalization, we simulate the spectra of the confined exciton states, their oscillator strengths and radiative lifetimes. We show that a single state of the confined exciton is optically active, which suggests that the MoS2/hBN nanobubble is a good candidate for the realisation of single-photon sources. Furthermore, the exciton binding energy, oscillator strength and radiative lifetime are enhanced due to the confinement effect.

cond-mat.mtrl-sci↗

arXiv2019

DFT+U Investigation of magnetocrystalline anisotropy of Mn-doped transition-metal dichalcogenides monolayers

Doped transition-metal dichalcogenides monolayers exhibit exciting magnetic properties for the benefit of two-dimensional spintronic devices. Using density functional theory (DFT) incorporating Hubbard-type of correction (DFT$+U$) to account for the electronic correlation, we study the magnetocrystalline anisotropy energy (MAE) characterizing Mn-doped MS$_2$ (M=Mo, W) monolayers. A single isolated Mn dopant exhibits a large perpendicular magnetic anisotropy of 35 meV (8 meV) in the case of Mn-doped WS$_2$ (MoS$_2$) monolayer. This value originates from the Mn in-plane orbitals degeneracy lifting due to the spin-orbit coupling. In pairwise doping, the magnetization easy axis changes to the in-plane direction with a weak MAE compared to single Mn doping. Our results suggest that diluted Mn-doped MS$_2$ monolayers, where the Mn dopants are well separated, could potentially be a candidate for the realization of ultimate nanomagnet units.

cond-mat.mtrl-sci↗

arXiv2019

Dependence of the magnetic interactions in MoS$_2$ monolayer on Mn-doping configurations

Understanding the magnetic properties of the various Mn doping configurations that can be encountered in $2H$-MoS$_2$ monolayer could be beneficial for its use in spintronics. Using density functional theory plus Hubbard U (DFT$+$U) approach, we study how a single isolated, double- and triple-substitution configurations of Mn atoms within a MoS$_2$ monolayer could contribute to its total magnetization. We find that the doping-configuration plays a critical role in stabilizing a ferromagnetic state in a Mn-doped MoS$_2$ monolayer. Indeed, the Mn-Mn magnetic interaction is found to be ferromagntic and strong for Mn in equidistant substitution positions where the separation average range of 6-11 Å. The strongest ferromagnetic interaction is found when substitutions are in second nearest neighbors Mo-sites of the armchair chain. Clustering is energetically favorable but it strongly reduces the ferromagnetic exchange energies. Our results suggest that ordering the Mn dopants on MoS$_2$ monolayer is needed to increase its potential ferromagnetism.

cond-mat.mtrl-sci↗

arXiv2018

Radiative lifetime of localized excitons in transition metal dichalcogenides

Disorder derived from defects or strain in monolayer TMDs can lead to a dramatic change in the physical behavior of the interband excitations, producing inhomogeneous spectral broadening and localization; leading to radiative lifetime increase. In this study, we have modeled the disorder in the surface of the sample through a randomized potential in monolayer WSe2. We show that this model allows us to simulate the spectra of localized exciton states as well as their radiative lifetime. In this context, we give an in depth study of the influence of the disorder potential parameters on the optical properties of these defects through energies, density of states, oscillator strengths, photoluminescence (PL) spectroscopy and radiative lifetime at low temperature (4K). We demonstrate that localized excitons have a longer emission time than free excitons, in the range of tens of picoseconds or more, and we show that it depends strongly on the disorder parameter and dielectric environment. Finally, in order to prove the validity of our model we compare it to available experimental results of the literature.

cond-mat.mes-hall↗