Articles de revues : « Electronic delocalisation »

1

Kahmann, Simon, Maria A. Loi et Christoph J. Brabec. « Delocalisation softens polaron electronic transitions and vibrational modes in conjugated polymers ». Journal of Materials Chemistry C 6, n^o 22 (2018) : 6008–13. http://dx.doi.org/10.1039/c8tc00909k.

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Men, Shuang, Peter Licence, Chi-Linh Do-Thanh, Huimin Luo et Sheng Dai. « X-ray photoelectron spectroscopy of piperidinium ionic liquids : a comparison to the charge delocalised pyridinium analogues ». Physical Chemistry Chemical Physics 22, n^o 21 (2020) : 11976–83. http://dx.doi.org/10.1039/d0cp01454k.

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Reibnegger, Gilbert. « An ab initio and density functional theory study on neutral pterin radicals ». Pteridines 26, n^o 4 (1 décembre 2015) : 135–42. http://dx.doi.org/10.1515/pterid-2015-0008.

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AbstractThe electronic structures of the five radicals resulting from homolytic elimination of one of the hydrogen atoms from the most stable tautomeric form of neutral pterin were investigated in gas phase as well as in aqueous solution. Molecular wave functions obtained by density functional theory were analysed by quantum theory of atoms in molecules and electron localisation functions (ELF). Spin densities of the radicals as well as electrostatic potential functions were analysed. Radicals resulting from elimination of N-bonded hydrogen atoms are more stable in comparison with radicals obtained after abstraction of C-bonded hydrogen atoms. N-centred radicals show strong delocalisation of spin density over both heteroaromatic rings; in C-centred radicals delocalisation does not occur. ELF analyses showed that in N-derived radicals particularly the lone electron pair at N2′ is strongly involved into the bicyclic heteroaromatic π-electron system. Thereby, bonding geometry at N2′ in these radicals changes from pyramidal to planar. Transition from gas phase to solution phase (water) generally leads to increased polarity of the structures. Pterin-derived free radicals have been implicated in several biologically important reactions; so this investigation provides first insights into the detailed electronic structures of such molecular systems.

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Schubert, Gerald, Alexander Weiße et Holger Fehske. « Delocalisation transition in chains with correlated disorder ». Physica B : Condensed Matter 359-361 (avril 2005) : 801–3. http://dx.doi.org/10.1016/j.physb.2005.01.232.

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Wu, Guanglu, István Szabó, Edina Rosta et Oren A. Scherman. « Cucurbit[8]uril-mediated pseudo[2,3]rotaxanes ». Chemical Communications 55, n^o 88 (2019) : 13227–30. http://dx.doi.org/10.1039/c9cc07144j.

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Martinez-Felipe, Alfonso, Fraser Brebner, Daniel Zaton, Alberto Concellon, Sara Ahmadi, Milagros Piñol et Luis Oriol. « Molecular Recognition via Hydrogen Bonding in Supramolecular Complexes : A Fourier Transform Infrared Spectroscopy Study ». Molecules 23, n^o 9 (6 septembre 2018) : 2278. http://dx.doi.org/10.3390/molecules23092278.

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We assess the assembly of supramolecular complexes by hydrogen bonding between azocompounds and a diacylaminopyridine monomer by temperature-dependent Fourier transform infrared spectroscopy (FT-IR) and density functional theory (DFT) calculations. The electronic delocalisation in the supramolecular rings formed by multiple hydrogen bonds stabilises the complexes, which coexist with dimeric species in temperature-dependent equilibria. We show how the application of readily available molecular modelling and spectroscopic techniques can predict the stability of new supramolecular entities coexisting in equilibria, ultimately assessing the success of molecular recognition.

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Vacher, Morgane, Fabio E. A. Albertani, Andrew J. Jenkins, Iakov Polyak, Michael J. Bearpark et Michael A. Robb. « Electron and nuclear dynamics following ionisation of modified bismethylene-adamantane ». Faraday Discussions 194 (2016) : 95–115. http://dx.doi.org/10.1039/c6fd00067c.

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We have simulated the coupled electron and nuclear dynamics using the Ehrenfest method upon valence ionisation of modified bismethylene-adamantane (BMA) molecules where there is an electron transfer between the two π bonds. We have shown that the nuclear motion significantly affects the electron dynamics after a few fs when the electronic states involved are close in energy. We have also demonstrated how the non-stationary electronic wave packet determines the nuclear motion, more precisely the asymmetric stretching of the two π bonds, illustrating “charge-directed reactivity”. Taking into account the nuclear wave packet width results in the dephasing of electron dynamics with a half-life of 8 fs; this eventually leads to the equal delocalisation of the hole density over the two methylene groups and thus symmetric bond lengths.

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Campo, Javier, Javier Luzón, Fernando Palacio, Garry J. McIntyre et Eric Ressouche. « Effect of spin delocalisation in K2FeCl5·H2O on its superexchange pathways ». Physica B : Condensed Matter 335, n^o 1-4 (juillet 2003) : 15–18. http://dx.doi.org/10.1016/s0921-4526(03)00181-9.

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Gilmour, J. T. A., et N. Gaston. « Design of superatomic systems : exploiting favourable conditions for the delocalisation of d-electron density in transition metal doped clusters ». Physical Chemistry Chemical Physics 22, n^o 33 (2020) : 18585–94. http://dx.doi.org/10.1039/d0cp01780a.

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Anikeenok, O. A., M. A. Augustyniak-Jab?okow, T. A. Ivanova, P. Reiche, R. Uecker et Yu V. Yablokov. « Delocalisation of the Cu2+ Unpaired Electron on the Next Nearest Ligands in LaSrGa0.995Cu0.005O4 Single Crystal ». physica status solidi (b) 226, n^o 1 (juillet 2001) : R1—R3. http://dx.doi.org/10.1002/1521-3951(200107)226:13.0.co;2-r.

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Hall, Michael R., Stephen A. Moggach et Paul J. Low. « Probing the Electronic Structure of Dinuclear Carbon-Rich Complexes Containing an Octa-3,5-diene-1,7-diyndiyl Bridging Ligand ». Inorganics 12, n^o 1 (1 janvier 2024) : 20. http://dx.doi.org/10.3390/inorganics12010020.

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One electron oxidation of the monometallic alkenylacetylide complexes [Ru{C≡CC(R)=CH2}(dppe)Cp*] (1) and [Ru{C≡CC(R)=CH2}Cl(dppe)2] (2) (R = Ph (a); R = 4-MeS-C6H4 (b)) generates in each case a dinuclear bis(allenylidene) complex [{Ru}2{μ-C=C=C(R)–CH2–H2C–(R)C=C=C}][PF6]2 ({Ru} = Ru(dppe)Cp* ([3a,b][PF6]2); {Ru} = RuCl(dppe)2 ([4a,b][PF6]2), containing an unsaturated ethane bridge between both allenylidene moieties. Deprotonation of this ethane bridge results in the formation of the previously reported octa-3,5-diene-1,7-diyndiyl-bridged bimetallic species [{Ru}2{μ-C≡CC(R)=CH–HC=(R)CC≡C}] ({Ru} = Ru(dppe)Cp* (5a,b); {Ru} = RuCl(dppe)2 (6a,b). The isolation of these complexes illustrates a general synthetic route to these conjugated bimetallic species from monomeric alkenylacetylide precursors. Electrochemical and spectroelectrochemical investigations evince the ready formation of the representative redox series [5a]n+, and TD-DFT calculations performed on optimised structures featuring the simplified {Ru(dmpe)Cp} coordination sphere [{Ru(dmpe)Cp}2{μ-C≡CC(Ph)=HC–CH(Ph)CC≡C}]n+ ([5a†]n+) (n = 0, 1, 2) reveal significant delocalisation of the unpaired charge in the formally mixed-valent species (n = 1), consistent with Class III assignment within the Robin–Day classification scheme.

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Chakraborty, S., et Mary N. L. « Review—An Overview on Supercapacitors and Its Applications ». Journal of The Electrochemical Society 169, n^o 2 (1 février 2022) : 020552. http://dx.doi.org/10.1149/1945-7111/ac5306.

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The efficient and sustainable use of energy is highly imperative to satisfy the escalating energy demands arising from the rapid commercialization of technologies. The development of novel electrochemical energy technologies is an essential aspect in the present-day scenario of rapid depletion of existing sources of energy. Conducting polymers are promising psuedocapacitive materials with an extended delocalisation network of π electrons, flexibility to functional modifications and facile intercalation and de-intercalation of electrolyte ions. These factors enable them to possess capacitances comparable with those of metal oxides. The use of copolymers in this context is noteworthy due to their diversity of combining different types of monomer units and facile integration. Carbon based materials have also been extensively employed on account of their high power densities and large number of charge-discharge cycles. The synergism of the non-faradaic double-layer capacitance with the faradaic charge transfer has the ability to provide impressive supercapacitor properties. Different types of polymer and polymer-composites based supercapacitors have been discussed with special emphasis on implantable biomedical devices and wearable electronics.

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Chisholm, Malcolm H., Robin J. H. Clark, Christopher M. Hadad et Nathan J. Patmore. « 3,6-Dioxypyridazine bridged tungsten–tungsten quadruple bonds. Comparisons of electron delocalisation with oxalate bridged compounds ». Chem. Commun., n^o 1 (2004) : 80–82. http://dx.doi.org/10.1039/b310982h.

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14

Argyriou, D. N., J. F. Mitchell, J. D. Jorgensen, J. B. Goodenough, P. G. Radaelli, D. E. Cox et H. N. Bordallo. « Structure and Magnetism in the Layered CMR Manganites La2-2xSr1+2xMn2O7 (x= 0·3, 0·4) ». Australian Journal of Physics 52, n^o 2 (1999) : 279. http://dx.doi.org/10.1071/p98105.

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In this paper we describe a detailed neutron diffraction investigation of the crystal and magnetic structure of two layered CMR manganites La1·2Sr1·8Mn2O7 (x = 0·4) and La1·4Sr1·6Mn2O7 (x = 0·3). In these materials of reduced dimensionality compared to the 3D perovskites, we find competing effects between charge-lattice and spin degrees of freedom. These effects can be investigated by studying the behaviour of crystal and magnetic structure as a function of temperature, composition and hydrostatic pressure. We find opposite lattice responses to the onset of charge delocalisation and magnetic ordering in these two layered compounds. Below the insulator-to-metal transition (TIM), the lattice response suggests that charge is transferred to d3z2-r2 orbitals in La1·2Sr1·8Mn2O7 and to dx2-y2 orbitals in La1·4Sr1·6Mn2O7. We argue that these changes are too large to be due to chemical differences. Instead we suggest that the orbital configuration of the Mn ion below TIM is sensitive to electronic doping. In La1·2Sr1·8Mn2O7 we find that the lattice response at TIM to be driven by lattice displacements that relax below TIM, consistent with polaronic degrees of freedom. We also note that the competition between super- and double-exchange to be significant in reduced dimensions. This is manifested in the change in the sign of the apical Mn-O bond compressibilities above and below TIM. Finally, we describe the magnetic structure of these two different layered manganites. We find that electronic doping also results in significant changes to the ordered arrangement of Mn spins. Interestingly the magnetism in reduced dimensions in these materials can be varied from relative simple structures that show ferromagnetic inter-bilayer coupling as observed in La1·2Sr1·8Mn2O7 to structures with antiferromagnetic inter-bilayer coupling as found in La1·4Sr1·6Mn2O7.

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Branscombe, Neil D. J., Andrew J. Atkins, Armando Marin-Becerra, Eric J. L. McInnes, Frank E. Mabbs, Jonathan McMaster et Martin Schröder. « Ni(iii) vs. Ni(ii)-thiyl radical : charge-delocalisation in a binuclear Ni(iii)Ni(ii)-dithiolate complex ». Chemical Communications, n^o 9 (2 avril 2003) : 1098–99. http://dx.doi.org/10.1039/b300245d.

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Butsch, Katharina, Alexander Haseloer, Simon Schmitz, Ingo Ott, Julia Schur et Axel Klein. « FeIII, CuII and ZnII Complexes of the Rigid 9-Oxido-phenalenone Ligand—Spectroscopy, Electrochemistry, and Cytotoxic Properties ». International Journal of Molecular Sciences 22, n^o 8 (12 avril 2021) : 3976. http://dx.doi.org/10.3390/ijms22083976.

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The three complexes [Fe(opo)3], [Cu(opo)2], and [Zn(opo)2] containing the non-innocent anionic ligand opo− (opo− = 9-oxido-phenalenone, Hopo = 9-hydroxyphenalonone) were synthesised from the corresponding acetylacetonates. [Zn(opo)2] was characterised using 1H nuclear magnetic resonance (NMR) spectroscopy, the paramagnetic [Fe(opo)3] and [Cu(opo)2] by electron paramagnetic resonance (EPR) spectroscopy. While the EPR spectra of [Cu(opo)2] and [Cu(acac)2] in dimethylformamide (DMF) solution are very similar, a rather narrow spectrum was observed for [Fe(opo)3] in tetrahydrofuran (THF) solution in contrast to the very broad spectrum of [Fe(acac)3] in THF (Hacac = acetylacetone, 2,4-pentanedione; acac− = acetylacetonate). The narrow, completely isotropic signal of [Fe(opo)3] disagrees with a metal-centred S = 5/2 spin system that is observed in the solid state. We assume spin-delocalisation to the opo ligand in the sense of an opo− to FeIII electron transfer. All compounds show several electrochemical opo-centred reduction waves in the range of −1 to −3 V vs. the ferrocene/ferrocenium couple. However, for CuII and FeIII the very first one-electron reductions are metal-centred. Electronic absorption in the UV to vis range are due to π–π* transitions in the opo core, giving Hopo and [Zn(opo)2] a yellow to orange colour. The structured bands ranging from 400 to 500 for all compounds are assigned to the lowest energy π−π* transitions. They show markedly higher intensities and slight shifts for the CuII (brown) and FeIII (red) complexes and we assume admixing metal contributions (MLCT for CuII, LMCT for FeIII). For both complexes long-wavelength absorptions assignable to d–d transitions were detected. Detailed spectroelectrochemical experiments confirm both the electrochemical and the optical assignments. Hopo and the complexes [Cu(opo)2], [Zn(opo)2], and [Fe(opo)3] show antiproliferative activities against HT-29 (colon cancer) and MCF-7 (breast cancer) cell lines in the range of a few µM, comparable to cisplatin under the same conditions.

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Albert, Alain, et Maxime A. Crener. « Les nouvelles politiques industrielles : Le cas des télécommunications ». Études internationales 14, n^o 3 (12 avril 2005) : 453–67. http://dx.doi.org/10.7202/701539ar.

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After showing the dynamic character of the world market of telecommunications equipment, the authors analyze the main factors which have contributed to the elaboration of the industrial structure in this field. Particular stress is laid on the role played by technological evolution as driving force of the industrial reorganization which is taking place right now in the field. This reorganization movement on a world scale has sometimes given rise, in industrial policy, to totally different behaviours from governments. Thus, the strategies of the Japanese and French branches are countered by measures taken by the US Government to deregulate and liberalize the market. The authors conclude by pointing out that, given the limited means at its disposal and faced with an international market of electronics threatened by competition from the Newly Industrialized Countries, there is a need for Canada to adopt a differential strategic approach which will allow it to acceed to technological sovereignty and to counter the delocalisation process which profit the NIC of South-East Asia.

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Blundo, Elena, Federico Tuzi, Salvatore Cianci, Marzia Cuccu, Katarzyna Olkowska-Pucko, Łucja Kipczak, Giorgio Contestabile et al. « Localisation-to-delocalisation transition of moiré excitons in WSe2/MoSe2 heterostructures ». Nature Communications 15, n^o 1 (5 février 2024). http://dx.doi.org/10.1038/s41467-024-44739-9.

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AbstractMoiré excitons (MXs) are electron-hole pairs localised by the periodic (moiré) potential forming in two-dimensional heterostructures (HSs). MXs can be exploited, e.g., for creating nanoscale-ordered quantum emitters and achieving or probing strongly correlated electronic phases at relatively high temperatures. Here, we studied the exciton properties of WSe2/MoSe2 HSs from T = 6 K to room temperature using time-resolved and continuous-wave micro-photoluminescence also under a magnetic field. The exciton dynamics and emission lineshape evolution with temperature show clear signatures that MXs de-trap from the moiré potential and turn into free interlayer excitons (IXs) for temperatures above 100 K. The MX-to-IX transition is also apparent from the exciton magnetic moment reversing its sign when the moiré potential is not capable of localising excitons at elevated temperatures. Concomitantly, the exciton formation and decay times reduce drastically. Thus, our findings establish the conditions for a truly confined nature of the exciton states in a moiré superlattice with increasing temperature and photo-generated carrier density.

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Yatsenko, A. V., K. A. Paseshnichenko et S. I. Popov. « Experimental and computational structural study of two hindered aminoanthraquinones in crystals and solutions ». Zeitschrift für Kristallographie - Crystalline Materials 215, n^o 9 (1 janvier 2000). http://dx.doi.org/10.1524/zkri.2000.215.9.542.

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The crystal and molecular structures of 2-methyl-1-methylamino-anthraquinone (I) and 1-methylphenylamino-anthraquinone (II) were studied by the X-ray single-crystal diffraction and the visible spectra of crystalline specimens and their solutions were recorded. The molecule I is closely planar, whereas in the molecule II the amino group is 58° rotated out of the plane of the anthraquinone skeleton. In both structures the molecules pack in stacks. The comparison of experimental and calculated (on the DFT and AM1 levels) molecular structures, together with the comparison of experimental and INDO/S-calculated electronic spectra, give the evidence that molecular conformations (especially for II) change upon transfer from the solid state to solutions, and the π-delocalisation throughout the whole molecule enhances in the solid state.

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20

Kenouche, Samir, Nassima Bachir, Wissem Bouchel et Jorge I. Martínez-Araya. « Aromaticity of six-membered nitro energetic compounds through molecular electrostatic potential, magnetic, electronic delocalisation and reactivity-based indices ». Journal of Molecular Graphics and Modelling, février 2024, 108728. http://dx.doi.org/10.1016/j.jmgm.2024.108728.

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Carlier, D., M. Ménétrier et C. Delmas. « Lithium deintercalation in LiNi0.30Co0.70O2 : Redox processes, electronic and ionic mobility as characterized by7Li MAS NMR and electrical properties ». MRS Proceedings 658 (2000). http://dx.doi.org/10.1557/proc-658-gg9.9.

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ABSTRACTLiNi1-yCoyO2 materials are particularly interesting as positive electrode in lithium-ion batteries. Their 7Li MAS NMR spectra are sensitive to the presence of paramagnetic Ni3+ cations as nearest and next-nearest neighbors. These contact shift (or Fermi contact) interactions are used to yield information on the lithium environment in terms of paramagnetic cations.Electrochemically deintercalated LixNi0.30Co0.70O2 phases have been characterized by XRD, 7Li MAS NMR, electronic conductivity and thermoelectronic power. Ni3+ oxidation to Ni4+ occurs at the beginning of deintercalation, leading to a Ni3+/Ni4+ hopping which causes an exchange of the 7Li NMR signals of the Li ions interacting with nickel. For higher deintercalation amounts, the signal due to Li ions with only cobalt as first and second neighbor is also involved in the exchange upon heating, showing the onset of ionic hopping. For x close to 0.70, an increase of the NMR shift with temperature is observed, which is assigned to a hopping between Ni4+ and Co3+. Therefore, the question as to which ion is actually oxidized during deintercalation is somewhat irrelevant around this composition. Finally, for x < 0.70, the presence of Ni hinders a true long-range electronic delocalisation between Co4+/Co3+ (LS) as it happens in LixCoO2(x < 0.70). However, electrons are clearly delocalized in restricted zones, as seen from NMR and thermoelectronic power coefficient.

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22

Pathak, Swati, Saurabh Singh, Syed Khalid, Kentaro Kuga, Tsunehiro Takeuchi et R. Bindu. « Orbital hybridisation effects in B2 phase Cr doped Co2MnAl ». Journal of Physics : Condensed Matter, 21 juin 2023. http://dx.doi.org/10.1088/1361-648x/ace092.

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Abstract We investigate here the magnetic, transport, local structural and electronic properties of Co$_2$Mn$_1$$_-$$_x$Cr$_x$Al (x=0, 0.05, 0.1 and 0.2). Our results show that all the compounds stabilise in B2 phase and are ferromagnets. The results reveal disorder at the structural and magnetic levels. X-ray absorption near edge structure (XANES) analysis reveal signature of antisite disorder between Mn and Al atoms with equal ratio. The electronic structure calculations suggest enhancement in the half metallicity, localisation of electrons at the Fermi level and an increment in density of states (DOS) with doping. The combined results of electronic structure calculations and XANES studies suggest transfer of electrons to the Co site. The results of high temperature resistivity measurements suggest the conduction electrons are undergoing transition from delocalisation to weak localisation to activated behaviour with Cr doping. The extended x-ray absorption spectroscopic (EXAFS) analysis shows that the local structure around Mn atom is different from the global structure as obtained from the x-ray diffraction results.The behaviour of the edge region is in line with the trend as obtained from the compositional analysis. We observe link between the hybridisation of 3$\emph{d}$ like states at the Mn, Cr sites with that at the Co site and the transport properties. This could help in understanding the unusual decrement in the lattice parameter with doping. These results reveal the role of local structure in understanding the physical properties of such systems.

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Kovaleva, N. N., F. V. Kusmartsev, A. B. Mekhiya, I. N. Trunkin, D. Chvostova, A. B. Davydov, L. N. Oveshnikov et al. « Control of Mooij correlations at the nanoscale in the disordered metallic Ta–nanoisland FeNi multilayers ». Scientific Reports 10, n^o 1 (décembre 2020). http://dx.doi.org/10.1038/s41598-020-78185-6.

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AbstractLocalisation phenomena in highly disordered metals close to the extreme conditions determined by the Mott-Ioffe-Regel (MIR) limit when the electron mean free path is approximately equal to the interatomic distance is a challenging problem. Here, to shed light on these localisation phenomena, we studied the dc transport and optical conductivity properties of nanoscaled multilayered films composed of disordered metallic Ta and magnetic FeNi nanoisland layers, where ferromagnetic FeNi nanoislands have giant magnetic moments of 10$$^3$$ 3 –10$$^5$$ 5 Bohr magnetons ($$\mu _{\mathrm{B}}$$ μ B ). In these multilayered structures, FeNi nanoisland giant magnetic moments are interacting due to the indirect exchange forces acting via the Ta electron subsystem. We discovered that the localisation phenomena in the disordered Ta layer lead to a decrease in the Drude contribution of free charge carriers and the appearance of the low-energy electronic excitations in the 1–2 eV spectral range characteristic of electronic correlations, which may accompany the formation of electronic inhomogeneities. From the consistent results of the dc transport and optical studies we found that with an increase in the FeNi layer thickness across the percolation threshold evolution from the superferromagnetic to ferromagnetic behaviour within the FeNi layer leads to the delocalisation of Ta electrons from the associated localised electronic states. On the contrary, we discovered that when the FeNi layer is discontinuous and represented by randomly distributed superparamagnetic FeNi nanoislands, the Ta layer normalized dc conductivity falls down below the MIR limit by about 60%. The discovered effect leading to the dc conductivity fall below the MIR limit can be associated with non-ergodicity and purely quantum (many-body) localisation phenomena, which need to be challenged further.

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« Foreword ». Australian Journal of Physics 52, n^o 2 (1999) : 151. http://dx.doi.org/10.1071/phv52n2_fo.

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In this paper we describe a detailed neutron diffraction investigation of the crystal and magnetic structure of two layered CMR manganites La1·2Sr1·8Mn2O7 (x = 0·4) and La1·4Sr1·6Mn2O7 (x = 0·3). In these materials of reduced dimensionality compared to the 3D perovskites, we find competing effects between charge-lattice and spin degrees of freedom. These effects can be investigated by studying the behaviour of crystal and magnetic structure as a function of temperature, composition and hydrostatic pressure. We find opposite lattice responses to the onset of charge delocalisation and magnetic ordering in these two layered compounds. Below the insulator-to-metal transition (TIM), the lattice response suggests that charge is transferred to d3z2-r2 orbitals in La1·2Sr1·8Mn2O7 and to dx2-y2 orbitals in La1·4Sr1·6Mn2O7. We argue that these changes are too large to be due to chemical differences. Instead we suggest that the orbital configuration of the Mn ion below TIM is sensitive to electronic doping. In La1·2Sr1·8Mn2O7 we find that the lattice response at TIM to be driven by lattice displacements that relax below TIM, consistent with polaronic degrees of freedom. We also note that the competition between super- and double-exchange to be significant in reduced dimensions. This is manifested in the change in the sign of the apical Mn-O bond compressibilities above and below TIM. Finally, we describe the magnetic structure of these two different layered manganites. We find that electronic doping also results in significant changes to the ordered arrangement of Mn spins. Interestingly the magnetism in reduced dimensions in these materials can be varied from relative simple structures that show ferromagnetic inter-bilayer coupling as observed in La1·2Sr1·8Mn2O7 to structures with antiferromagnetic inter-bilayer coupling as found in La1·4Sr1·6Mn2O7.

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Murphy, Cónal, Eoin P. O'Reilly et Christopher A. Broderick. « Theory and optimisation of radiative recombination in broken-gap InAs/GaSb superlattices ». Journal of Physics D : Applied Physics, 9 octobre 2023. http://dx.doi.org/10.1088/1361-6463/ad015d.

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Abstract We present a theoretical analysis of mid-infrared radiative recombination in InAs/GaSb superlattices (SLs). We employ a semi-analytical plane wave expansion method in conjunction with an 8-band k·p Hamiltonian to compute the SL electronic structure, paying careful attention to the identification and mitigation of spurious solutions. The calculated SL eigenstates are used directly to compute spontaneous emission spectra and the radiative recombination coefficient B. We elucidate the origin of the relatively large B coefficients in InAs/GaSb SLs which, despite the presence of spatiallyindirect (type-II-like) carrier confinement, are close to that of bulk InAs and compare favourably to those calculated for mid-infrared type-I pseudomorphic and metamorphic quantum well structures having comparable emission wavelengths. Our analysis explicitly quantifies the roles played by carrier localisation (specifically, partial delocalisation of bound electron states) and miniband formation (specifically, miniband occupation and optical selection rules) in determining the magnitude of B and its temperature dependence. We perform a high-throughput optimisation of the room temperature B coefficient in InAs/GaSb SLs across the 3.5 – 7 μm wavelength range, quantifying the dependence of B on the relative thickness of the electron-confining InAs and hole-confining GaSb layers. This analysis provides guidance for the growth of optimised SLs for mid-infrared light emitters. Our results, combined with the expected low non-radiative Auger recombination rates in structures having spatially indirect electron and hole confinement, corroborate recently observed high output power in prototype InAs/GaSb SL inter-band cascade light-emitting diodes.

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Articles de revues sur le sujet « Electronic delocalisation »

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