http://dspace.univ-chlef.dz/handle/123456789/289 Université Hassiba Benbouali de Chlef / Faculté des sciences Sun, 05 Apr 2026 22:02:20 GMT 2026-04-05T22:02:20Z http://localhost:80/bitstream/id/5ea7fdbb-3cc9-4667-9ab7-fb5905d5ea66/ http://dspace.univ-chlef.dz/handle/123456789/289 http://dspace.univ-chlef.dz/handle/123456789/2203 Study of thermo-photovoltaic cells based on quantum nanostructures of III-V materials TRAICHE, MOHAMMED In this work, we investigate the performance of a new generation of thermo-photovoltaic (TPV) cells engineered from hybrid quantum nanostructures based on III–V semiconductor materials. The main objective of our research is to exploit the synergistic integration of narrow band-gap antimonides with the unique optoelectronic properties of III–V alloys, thereby enabling ultrabroadband absorption extending from the visible to the far-infrared domain. This spectral versatility opens the pathway for significantly enhanced photoelectric conversion efficiency, surpassing the limits of conventional photovoltaic technologies. The novelty of this study lies in the nanotechnology-driven design of the active medium: by tailoring the dimensional confinement of carriers in 0D quantum dots, 1D quantum wires, and 2D quantum wells, it becomes possible to precisely control absorption, carrier transport, and thermal management. Such nanostructuration not only broadens the optical response but also enhances phonon scattering and thermal stability, key challenges in high-performance TPV systems. The proposed approach thus provides a multifunctional platform that unites photovoltaic and thermoelectric effects within a single hybrid device, this research demonstrates a pathway toward highly efficient, spectrally versatile, and thermally robust energy conversion devices, positioning hybrid nanostructured TPVs as a disruptive technology in the future of renewable and sustainable energy. Wed, 01 Jan 2025 00:00:00 GMT http://dspace.univ-chlef.dz/handle/123456789/2203 2025-01-01T00:00:00Z http://dspace.univ-chlef.dz/handle/123456789/2162 Etude ab-initio des propriétés structurales, magnéto-électroniques des alliages d’Heusler quaternaires NOURINE, RACHIDA In this work, the structural, electronic and magnetic properties of some quaternary Heusler alloys (QH) based on RhCo were calculated using an ab-initio method. These compounds can be generated from doping of the ternary Heusler compounds; in this case, we begin our study by following the variation of structural, electronic and magnetic properties of Cobalt-doped of Rh2MnSn. The Co-substitution at Rh sites of Rh2-xCoxMnSn (x = 0 to 2) transforms it to half metallic material from the concentrations more than x=0,75. The magnetic properties reveal that the Co-doping increases the total magnetic moment; it is equal to 4.68 μB for Rh2MnSn to reach 5 μB in the range of half-metallic compounds founds. This integer value is obeying the Slater Pauling behavior with a 100% spin polarization. The exchange interaction parameters ( jij) and the Curie temperatures (Tc) of RhCoMnZ (Z = Al, Si, Ga, Ge, Sn, Sb) are also estimated, using the LMTO method implemented in the Questaal package. The Tc is calculated with mean field approximation (MFA), it is higher than ambient temperature for all compounds studied making them promising candidates for spintronic devices. Mon, 30 Jun 2025 00:00:00 GMT http://dspace.univ-chlef.dz/handle/123456789/2162 2025-06-30T00:00:00Z http://dspace.univ-chlef.dz/handle/123456789/2157 Etude ab-initio des propriétés structurales, magnéto-électroniques des alliages d’Heusler quaternaires NOURINE, RACHIDA Dans ce travail, les propriétés structurelles, électroniques et magnétiques de certains alliages de heusler quaternaire (QH) basées sur RhCo ont été calculées à l'aide d'une méthode ab-initio. Ces composés peuvent être générés par le dopage des composés heusler ternaires; dans ce cas, nous commençons notre étude en suivant la variation des propriétés structurelles, électroniques et magnétiques des Rh2MnSn dopés au cobalt. La substitution du Co aux sites Rh de Rh2-xCoxMnSn (x = 0 à 2) le transforme en un matériau demi-métallique pour les concentrations supérieures à x = 0,75. Les propriétés magnétiques révèlent que le Co augmente le moment magnétique total; il est égal à 4,68 μB pour que Rh2MnSn et atteigne 5 μB pour le reste des composés demi-métalliques trouvés. Cette valeur entière obéissait au comportement SlaterPauling avec une polarisation de spin de 100%. Les paramètres d'interaction d'échange (jij) et les températures Curie (TC) de RhCoMnZ (Z = Al, Si, Ga, Ge, Sn, Sb) sont estimés, en utilisant la méthode LMTO implémentée dans le package Questaal. La TC est calculé avec l’approximation du champ moyen (MFA), il est plus élevé que la température ambiante pour tous les composés étudiés, ce qui en fait des candidats prometteurs pour les dispositifs spintroniques. Mon, 30 Jun 2025 00:00:00 GMT http://dspace.univ-chlef.dz/handle/123456789/2157 2025-06-30T00:00:00Z http://dspace.univ-chlef.dz/handle/123456789/2110 DYNAMICS OF BINARY MIXTURES AT ULTRA COLD TEMPERATURES: EFFECTS OF INTERSPECIES CORRELATIONS MEHEDI, Atika This do ctoral work intends to take account of dynamical correlations in binary mixtures of Bose-Ein stein condensates (BEC), comp osed of two distinct sp ecies. In a p rel imi nary analysis, we consider a purely one-dimensional mixture, where the anomalous (or off-diagonal) correlations are finite and do not requ ire any renormalization. Their b ehavior, examined within a variational framework usin g a gau ssian density op erator, corrob orate a preceding result assessing that the anomalous and non cond ensate densities are of the same order and, therefore, any approach con sidering only non condensate densities can only b e viabl e at very low temp erature (or zero temp erature) or near the transition. This was demonstrated numerically by solving a set of self-consistent equations. Furthermore, in a binary mixture, a set of unprecedented correlations app ears . Indeed, b eside the intras p ecies correlations, we shed light on intersp ecies correlations, which depict the entanglement b etween the sp ecies In the vaste literature, we noticed that these effects are generally omitted owing to the fact that, in many exp eriments, the entanglement b etween different sp ecies is considered as marginal. We show however in this work, that it n eed s not b e the case in a general context. These effects are however quite tiny and cannot b e observed in situations where the mean field is dominant. Hence, we considered situations where the mean -field is almost zero. This fortunately happ ens for a binary system when the intersp ecies interactions are attractive an d almost neutralize the interasp ecies ones. This lead s to self-b oun d states named droplets which were indeed dis covered exp eri mentally. We therefore fo cused on droplets in quasi-one dimensional geometries and exhibited the dominant role of intersp ecies fluctuations. We showed that the droplet states are more stable and therefore more easily ob servable when one includes intersp ecies correlations. We also show that these effects add up to the LHY contributions extending th e b eyond mean-field theory in the Bogoliub ov framework. This work was p erformed in a consistent and metho dic way which led to original results published in journal of low temp erature physics A Thesis Submitted For Degree of Doctor in Theoretical physics Wed, 01 Jan 2025 00:00:00 GMT http://dspace.univ-chlef.dz/handle/123456789/2110 2025-01-01T00:00:00Z