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Aharonov-Bohm caging is a localization mechanism stemming from the competition between the geometry and the magnetic field. Originally described for a tight-binding model in the dice lattice, this destructive interference phenomenon prevents any wavepacket spreading away from a strictly confined region. Accordingly, for the peculiar values of the field responsible for this effect, the energy spectrum consists of a discrete set of highly degenerate flat bands. In the present work, we show that Aharonov-Bohm cages are also found in an infinite set of hyperbolic dice tilings defined on a negatively curved hyperbolic plane. We detail the construction of these tilings and compute their Hofstadter butterflies by considering periodic boundary conditions on high-genus surfaces. As recently observed for some regular hyperbolic tilings, these butterflies do not manifest the self-similar structure of their Euclidean counterparts but still contain some gaps. We also consider the energy spectrum of hyperbolic kagome tilings (which are the dual of hyperbolic dice tilings), which displays interesting features, such as highly degenerate states arising for some particular values of the magnetic field. For these two families of hyperbolic tilings, we compute the Chern number in the main gaps of the Hofstadter butterfly and propose a gap labeling inspired by the Euclidean case. Finally, we also study the triangular Husimi cactus, which is a limiting case in the family of hyperbolic kagome tilings, and we derive an exact expression for its spectrum versus magnetic flux., Comment: 15 pages, 10 figures, published version

Using a description of the Levin-Wen model excitations in terms of Wilson lines, we compute the degeneracy of the energy levels for any input anyon theory and for any trivalent graph embedded on any (orientable) compact surface. This result allows one to obtain the finite-size and finite-temperature partition function and to show that there are no thermal phase transitions., Comment: 7 pages, 2 figures, published version

International audience; Radiation-induced segregation (RIS) of solutes in materials exposed to irradiation is a well-known problem.It affects the lifetime of nuclear reactor core components by favoring radiation-induced degradation phenomena such as hardening and embrittlement. In this work, RIS tendencies in face centered cubic (fcc) Ni-X (X = Cr, Fe, Ti, Mn, Si, P) dilute binary alloys are examined. The goal is to investigate the driving forces and kinetic mechanisms behind the experimentally observed segregation. By means of ab initio calculations, point-defect stabilities and interactions with solutes are determined, together with migration energies and attempt frequencies.Transport and diffusion coefficients are then calculated in a mean-field framework, to get a full picture of solutedefect kinetic coupling in the alloys. Results show that all solutes considered, with the exception of Cr, prefer vacancy-mediated over interstitial-mediated diffusion during both thermal and radiation-induced migration. Cr, on the other hand, preferentially migrates in a mixed-dumbbell configuration. P and Si are here shown to be enriched, and Fe and Mn to be depleted at sinks during irradiation of the material. Ti and Cr, on the other hand, display a crossover between enrichment at lower temperatures, and depletion in the higher temperature range.Results in this work are compared with previous studies in body centered cubic (bcc) Fe, and discussed in the context of RIS in austenitic alloys.

We study the Wegner-Wilson loops in the string-net model of Levin and Wen in the presence of a string tension. The latter is responsible for a phase transition from a topological deconfined phase (weak tension) to a trivial confined phase (strong tension). We analyze the behavior of all Wegner-Wilson loops in both limiting cases for an arbitrary input theory of the string-net model. Using a fluxon picture, we compute perturbatively the first contributions to a perimeter law in the topological phase as a function of the quantum dimensions. In the trivial phase, we find that Wegner-Wilson loops obey a modified area law, in agreement with a recent mean-field approach., 5 pages, 3 figures, published version

In two dimensions, topological phases of free Majorana fermions coupled to a $\mathbb{Z}_2$ gauge field are known to be classified according to the Chern number $\nu \in \mathbb{Z}$. Its value mod 16 specifies the type of anyonic excitations. In this paper, we investigate triangular vortex configurations (and their dual) in the Kitaev honeycomb model and show that fourteen of these sixteen phases can be obtained by adding a time-reversal symmetry-breaking term. Missing phases are $\nu=\pm 7$. More generally, we prove that any periodic vortex configuration with an odd number of vortices per geometric unit cell can only host even Chern numbers whereas odd Chern numbers can be found in other cases., Comment: 15 pages, 21 figures, minor typos corrected

International audience; Alors que les budgets dans les sections de Recherche et Développement en entreprise augmentent d’année en année, il convient de se demander si les stratégies utilisées pour développer la créativité sont réellement efficaces. Bien souvent en entreprise, le travail créatif se fait dans le cadre de collaboration en équipes où sont réunis des individus provenant d’horizons différents, que ce soit sur des aspects démographiques (par ex., l’âge) ou plus discrets (par ex., l’éducation). Si la raison évidente de cette mixité est de promouvoir et de confronter une pluralité des regards sur le problème posé, les données issues de la littérature scientifique laissent paraître un enthousiasme plus réservé. Dans cette revue théorique, nous proposons de récapituler les grandes lignes de l’histoire scientifique de la créativité et notamment de son attribution au seul domaine des capacités de l’individu, pour aboutir à une prise en compte de l’environnement social (Amabile, 1983). Nous traiterons ensuite de l’application de ce changement de perspective au travers d’un questionnement sur la gestion de la diversité quand un effort créatif collectif est attendu. L’objectif poursuivi étant de mettre en relief l’importance de moduler la stratégie de gestion de l’équipe en fonction des étapes d’avancement du projet créatif, selon qu’il soit attendu de produire quelque chose de nouveau, en début de projet, ou quelque chose d’utile, en fin de projet

International audience; From a systematic atom probe tomography (APT) characterization of the radiation-induced segregation (RIS) in dilute Fe-Ni and Ni-Ti model alloys, we highlight fluctuations of the solute local concentration up to the scale of the APT specimens. We deduce the RIS at dislocation loops from a solute diffusion equation, that is solved at steady state, within the Voronoi's volume occupied by a single loop. From a statistical sampling of the Voronoi's volume and the dislocation loop radius modeled after the characterization of the microstructure by transmission electron microscopy, we provide the full RIS distribution. The present statistical approach of RIS demonstrates that the fluctuation of local solute concentrations in Fe-Ni and Ni-Ti mainly results from the dispersion in size and density of the dislocation loop population. Besides, we highlight the impact of the post-treatment parameters used in the APT protocol on the extracted RIS profiles. In Ni-Ti alloys, the simulated Ti-depletion profiles are in very good agreement with the measured ones. Furthermore, the dispersion of the loop radius and density is shown to play a critical role on the fluctuations of the Ti local concentration. In Fe-Ni, the identification of discrepancies between the simulated Ni-enrichment profiles and the measured ones provides a signature of additional operating mechanisms of the solute redistribution, such as radiation-induced precipitation.

International audience; Une première étude analyse un corpus de photographies illustrant des articles de presse relatifs aux migrants. L’analyse met en évidence un motif dominant dans la manière de montrer les migrants. Ce sont des hommes, en groupe important, photographiés en extérieur et de jour. Dans une seconde étude, on demande à 88 participants d’estimer la représentativité des photographies du corpus. On constate que ce sont les photographies montrant le motif dominant dans sa totalité qui sont jugées les plus représentatives des migrants. Ces résultats sont discutés dans le cadre de la théorie des représentations sociales et au regard de la notion d’objectivation.

Because virtual reality seems to be increasingly considered in different medical fields, the objective of this study is to define the optimal conditions for its use in a population of elderly women with breast cancer. By using a questionnaire, we evaluated the interest but also the immersive aspirations and preferences of elderly women with regard to this innovative device, taking into account the possible changes with age (60-65 years; 66-69, 70 and over). Surprisingly, older people - whatever the age group - are particularly favorable to virtual reality without actually having experienced it. The patients primarily chose immersion in a natural environment (with a marked preference for mountain landscapes) accompanied by musical background or even guided relaxation. However, because they judged important to remain focused on the treatments, the patients especially expect VR to regulate their negative emotions (lowering anxiety) and to allow them to escape from the painful contingencies of the real. Thus, virtual reality must take them into a magical world, which is more salient than to distract them or make them laugh. The distracting power, commonly associated with VR, does not seem to be the most popular reason to use with seniors facing medical care.

We present a fully inkjet-printed flexible thermoelectric device using organic and organic/inorganic hybrid materials. As part of our effort in the development of an n-type material, we present an approach to synthesize a solution processable thermoelectric hybrid material based on in situ oxidative polymerization and intercalation that can yield layered quasi two-dimensional superlattice structures. Thus, we have inserted poly(3,4-ethylenedioxythiophene) (PEDOT) within the nanotemplates of vanadium pentoxide gel (V2O5·nH2O) in order to enhance the charge carrier concentration. Furthermore, for the first time, we adapted the hybrid (PEDOT)xV2O5 material to the inkjet printing technology, thus successfully proving the printability of (PEDOT)xV2O5. Hence, we successfully produced a thermoelectric device composed of 4 thermocouples. Moreover, we optimized the geometry of the organic thermoelectric generator (OTEG) device thanks to a numerical model; the simulated and measured results are presented. The OTEG yielded a power density as high as 0.266 μW cm−2 for a temperature gradient of 20 K, therefore unveiling the potential of hybrid V2O5-based compounds for thermoelectric applications.

On the basis of the melt and quench strategy, over 3000 structurally different AlOx structures have been generated using ab initio molecular dynamics. Unlike other previous studies where defects were introduced into some crystalline polymorph of Al2O3, a variety of defects emerged directly from this approach. A new way to probe the short (distances between first neighbors and coordination numbers) and medium (atom rings, bond angles, and distances between second neighbors) range structural properties of H- and/or O-rich AlOx has been defined. The evolution of such structural properties during the densification process with mass loss has been studied using averaged data at a fixed chemical composition. A good agreement is observed between experimental and theoretical structural data, validating the methodology. In particular, the profile of the total experimental neutron pair correlation function has been rationalized. At fixed composition, the Spearman correlations have been calculated in order to reveal ...

We use a recently proposed class of tensor-network states to study phase transitions in string-net models. These states encode the genuine features of the string-net condensate such as, e.g., a nontrivial perimeter law for Wilson loops expectation values, and a natural order parameter detecting the breakdown of the topological phase. In the presence of a string tension, a quantum phase transition occurs between the topological phase and a trivial phase. We benchmark our approach for $\mathbb{Z}_2$ string nets and capture the second-order phase transition which is well known from the exact mapping onto the transverse-field Ising model. More interestingly, for Fibonacci string nets, we obtain first-order transitions in contrast with previous studies but in qualitative agreement with mean-field results., 10 pages, 3 figures

International audience; Flexible and lightweight printed thermoelectric devices are becoming increasingly attractive with the advent of ubiquitous sensing and within the context of an increasing energy demand and the associated environmental issues. In this study, flexible thermoelectric devices based on efficient solution-processed organic/hybrid thermoelectric materials have been successfully patterned. The n-type component hexylammonium titanium disulfide (TiS2(HA)x) nanocomposite reaches a ZT of 0.08 ± 0.06 at room temperature and was successfully printed on a flexible substrate using inkjet technology which yielded a functional device. The device operates in a near-ambient temperature range and retains its performance under mechanical bending, demonstrating thus the flexible properties of the device.

We study the energy spectrum of a two-dimensional electron in the presence of both a perpendicular magnetic field and a potential. In the limit where the potential is small compared to the Landau level spacing, we show that the broadening of Landau levels is simply expressed in terms of the structure factor of the potential. For potentials that are either periodic or random, we recover known results. Interestingly, for potentials with a dense Fourier spectrum made of Bragg peaks (as found, e.g., in quasicrystals), we find an algebraic broadening with the magnetic field characterized by the hyperuniformity exponent of the potential. Furthermore, if the potential is self-similar such that its structure factor has a discrete scale invariance, the broadening displays log-periodic oscillations together with an algebraic envelope., 13 pages, 3 figures, published version

The aim of this work is to produce via a low cost technique a thin film of ZnO showing optoelectronics properties similar to those one could obtain through various vacuum techniques. In order to achieve such goal, electrodeposition appears to be one of the most interesting approaches. Employing such technique in a Cl-containing bath, a high doping of the ZnO layer can be readily achieved through the substitution of a chloride ion for an oxygen atom in the ZnO lattice: the obtained optoelectronic properties are comparable to the ones of vacuum deposited layer. However, the introduction of chloride was found to be difficult to control, leading to a high concentration of inactive chloride in the ZnO lattice and, as a result, lower electrical performances of the material. In this study, the limitation of chloride doping is evidenced and explained considering the formation of chloride rich compounds. Moreover, ab initio calculations demonstrate that incorporation of perchlorate ions in the ZnO lattice at an ox...

Cu2ZnSn(S1–xSex)4 (CZTSSe) alloys are promising candidates for low-cost and high-efficiency thin-film solar cells. Compared to CdTe and Cu(InxGa1–x)Se2, CZTSSe uses chemicals found more abundantly on earth. This key aspect as well as its optical properties—band gap range of 1.0–1.5 eV and absorption coefficient larger than 104 cm–1—makes CZTSSe a feasible option for photovoltaic thin-film technologies scalable to TW/year. The key limitation to high efficiency in this technology remains a deficit in the open-circuit voltage with respect to the band gap: many groups have linked this drawback of CZTSSe solar cells to the presence of minor phases. This review aims to summarize what is known about CZTSSe minor phases and their impact on device characteristics.

We consider the string-net model obtained from $SU{(2)}_{2}$ fusion rules. These fusion rules are shared by two different sets of anyon theories. In this paper, we study the competition between the two corresponding non-Abelian quantum phases in the ladder geometry. A detailed symmetry analysis shows that the nontrivial low-energy sector corresponds to the transverse-field cluster model that displays a critical point described by the $so{(2)}_{1}$ conformal field theory. Other sectors are obtained by freezing spins in this model.

Two-dimensional tight-binding models for quasicrystals made of plaquettes with commensurate areas are considered. Their energy spectrum is computed as a function of an applied perpendicular magnetic field. Landau levels are found to emerge near band edges in the zero-field limit. Their existence is related to an effective zero-field dispersion relation valid in the continuum limit. For quasicrystals studied here, an underlying periodic crystal exists and provides a natural interpretation to this dispersion relation. In addition to the slope (effective mass) of Landau levels, we also study their width as a function of the magnetic flux per plaquette and identify two fundamental broadening mechanisms: (i) tunneling between closed cyclotron orbits and (ii) individual energy displacement of states within a Landau level. Interestingly, the typical broadening of the Landau levels is found to behave algebraically with the magnetic field with a nonuniversal exponent., Comment: 14 pages, 9 figures

National audience; Épidaure Market est un supermarché virtuel qui aborde avec les jeunes l’influence des techniques de vente, de la publicité, des pairs et de la famille sur les choix de consommation. Une évaluation de ce dispositif montre qu’Épidaure Market atteint ses objectifs en augmentant significativement ces connaissances chez les scolaires.

Herein we report a theoretical investigation based on density-functional theory (DFT) calculations devoted to the nature of charge carriers in $\mathrm{CdI}{\mathrm{n}}_{2}{\mathrm{S}}_{4}$. Our simulations led to unambiguous results concerning the origin of $n$-type semiconductivity and its magnitude in this material. Namely, the calculated defect formation energies demonstrate that the cadmium substoichiometry is more favorable than the indium one to account for $n$-type conductivity. Moreover, the anionic vacancies would not be the driving force of the occurring processes but a sulfur-poor atmosphere has to be privileged compared to a sulfur-rich one to favor the formation of $\mathrm{CdI}{\mathrm{n}}_{2}{\mathrm{S}}_{4}$ with understoichiometry in Cd(II) and thus achieve a higher concentration of free electrons at room temperature.

The search for functional materials is currently hindered by the difficulty to find significant correlation between constitutive properties of a material and its functional properties. In the case of amorphous materials, the diversity of local structures, chemical composition, impurities and mass densities makes such a connection difficult to be addressed. In this Letter, the relation between refractive index and composition has been investigated for amorphous AlOx materials, including nonstoichiometric AlOx, emphasizing the role of structural defects and the absence of effect of the band gap variation. It is found that the Newton–Drude (ND) relation predicts the refractive index from mass density with a rather high level of precision apart from some structures displaying structural defects. Our results show especially that O- and Al-based defects act as additive local disturbance in the vicinity of band gap, allowing us to decouple the mass density effects from defect effects (n = n[ND] + Δndefect).

In this paper we present a new software, Python for Defect Energy Formation (PyDEF), especially dedicated to the calculation of defect formation energy including its various corrections as developed by the theoretical community through the years. This program offers an intuitive graphical user interface which allows one to easily compute the corrected formation energy of any defect using theoretical calculation results. PyDEF is particularly suited for semiconductor materials as it includes finite size error corrections due to spurious intercell interactions as it is able to plot the formation energy of the different charge states and to determine the more stable ones as a function of the Fermi energy. Moreover PyDEF is able to plot Density Of States (DOS) with various parameters such as the projection on atoms or atomic species allowing a more comprehensive representation of defect-related electronic states. This software is developed in such a way that even non specialist or coder can use it and easily and quickly obtain reliable results.

Formation entropy of point defects is one of the last crucial elements required to fully describe the temperature dependence of point defect formation. However, while many attempts have been made to compute them for very complicated systems, very few works have been carried out such as to assess the different effects of finite size effects and precision on such quantity. Large discrepancies can be found in the literature for a system as primitive as the silicon vacancy. In this work, we have proposed a systematic study of formation entropy for silicon vacancy in its 3 stable charge states: neutral, +2 and –2 for supercells with size not below 432 atoms. Rationalization of the formation entropy is presented, highlighting importance of finite size error and the difficulty to compute such quantities due to high numerical requirement. It is proposed that the direct calculation of formation entropy of VSi using first principles methods will be plagued by very high computational workload (or large numerical errors) and finite size dependent results.

Copper nitrides are defect-tolerant semiconductors with properties that are promising for solar energy conversion applications. Currently, there are few known ternary copper nitride materials. Here, we synthesized a previously unreported CuNbN2 using an ion-exchange reaction and subsequently determined its properties. CuNbN2 has a layered delafossite-type structure with NbN6 octahedra arranged in layers separated by linear N–Cu–N bonds. Experimental measurements and theoretical calculations agree that CuNbN2 has a 1.3–1.4 eV optical absorption threshold; theory also indicates that the lowest energy indirect band gap is 0.9 eV. The calculated CuNbN2 electron and hole effective masses are quite isotropic (mout /min = 1.3–2.1) and low (m = 0.3–0.7 me), as for the layered crystal structure. On the basis of these results, we propose a new lattice-matched delafossite tandem solar cell approach with Cu(Nb,Ta)N2 absorbers, p-type CuAlO2 contacts, and n-type ZnO contacts. Interestingly, first-principles calculatio...

Defect tolerance is the tendency of a semiconductor to keep its properties despite the presence of crystallographic defects. Scientific understanding of the origin of defect tolerance is currently missing. Here we show that semiconductors with antibonding states at the top of the valence band are likely to be tolerant to defects. Theoretical calculations demonstrate that Cu3N with antibonding valence band maximum has shallow intrinsic defects and no surface states, in contrast to GaN with bonding valence band maximum. Experimental measurements indicate shallow native donors and acceptors in Cu3N thin films, leading to 10(16)-10(17) cm(-3) doping with either electrons or holes depending on the growth conditions. The experimentally measured bipolar doping and the solar-matched optical absorption onset (1.4 eV) make Cu3N a promising candidate absorber for photovoltaic and photoelectrochemical solar cells, despite the calculated indirect fundamental band gap (1.0 eV). These conclusions can be extended to other materials with antibonding character of the valence band, defining a class of defect-tolerant semiconductors for solar energy conversion applications.

The energy spectrum of a tight-binding Hamiltonian is studied for the two-dimensional quasiperiodic Rauzy tiling in a perpendicular magnetic field. This spectrum known as a Hofstadter butterfly displays a very rich pattern of bulk gaps that are labeled by four integers, instead of two for periodic systems. The role of phason-flip disorder is also investigated in order to extract genuinely quasiperiodic properties. This geometric disorder is found to only preserve main quantum Hall gaps., 9 pages, 5 figures, published version

Cu2ZnSn(S1–xSex)4 (CZTSSe) alloys are promising candidates for low-cost and high-efficiency thin-film solar cells. Compared to CdTe and Cu(InxGa1–x)Se2, CZTSSe uses chemicals found more abundantly on earth. This key aspect as well as its optical properties—band gap range of 1.0–1.5 eV and absorption coefficient larger than 104 cm–1—makes CZTSSe a feasible option for photovoltaic thin-film technologies scalable to TW/year. The key limitation to high efficiency in this technology remains a deficit in the open-circuit voltage with respect to the band gap: many groups have linked this drawback of CZTSSe solar cells to the presence of minor phases. This review aims to summarize what is known about CZTSSe minor phases and their impact on device characteristics.

We present a detailed study of local and nonlocal correlations in the electronic structure of elemental transition metals carried out by means of the quasiparticle self-consistent GW ($\mathrm{QS}\mathit{GW}$) and dynamical mean field theory (DMFT). Recent high resolution ARPES and Haas-van Alphen data of two typical transition metal systems (Fe and Ni) are used as a case study. (i) We find that the properties of Fe are very well described by $\mathrm{QS}\mathit{GW}$. Agreement with cyclotron and very clean ARPES measurements is excellent, provided that final-state scattering is taken into account. This establishes the exceptional reliability of $\mathrm{QS}\mathit{GW}$ also in metallic systems. (ii) Nonetheless $\mathrm{QS}\mathit{GW}$ alone is not able to provide an adequate description of the Ni ARPES data due to strong local spin fluctuations. We surmount this deficiency by combining nonlocal charge fluctuations in $\mathrm{QS}\mathit{GW}$ with local spin fluctuations in DMFT. (iii) Finally we show that the dynamics of the local fluctuations are actually not crucial. The addition of an external static field can lead to similarly good results if nonlocal correlations are included through $\mathrm{QS}\mathit{GW}$.

We discuss the emergence of bound states in the low-energy spectrum of the string-net Hamiltonian in the presence of a string tension. In the ladder geometry, we show that a single bound state arises either for a finite tension or in the zero-tension limit depending on the theory considered. In the latter case, we perturbatively compute the binding energy as a function of the total quantum dimension. We also address this issue in the honeycomb lattice where the number of bound states in the topological phase depends on the total quantum dimension. Finally, the internal structure of these bound states is analyzed in the zero-tension limit., 5 pages, 3 figures, published version

We introduce a quantum dimer model on the hexagonal lattice that, in addition to the standard three-dimer kinetic and potential terms, includes a competing potential part counting dimer-free hexagons. The zero-temperature phase diagram is studied by means of quantum Monte Carlo simulations, supplemented by variational arguments. It reveals some new crystalline phases and a cascade of transitions with rapidly changing flux (tilt in the height language). We analyze perturbatively the vicinity of the Rokhsar-Kivelson point, showing that this model has the microscopic ingredients needed for the "devil's staircase" scenario [E. Fradkin et al., Phys. Rev. B 69, 224415 (2004)], and is therefore expected to produce fractal variations of the ground-state flux., Comment: Published version. 5 pages + 8 (Supplemental Material), 31 references, 10 color figures

We present ab initio calculations of the electronic structure and the optical properties of wurtzite Si (Si-IV). We find an indirect band gap of 0.95 eV (Gamma(5) -> M-1) and an optically forbid ...

We study a string-net ladder in the presence of a string tension. Focusing on the simplest non-Abelian anyon theory with a quantum dimension larger than two, we determine the phase diagram and find a Russian doll spectrum featuring size-independent energy levels as well as highly degenerate zero-energy eigenstates. At the self-dual points, we compute the gap exactly by using a mapping onto the Temperley-Lieb chain. These results are in stark constrast with the ones obtained for Fibonacci or Ising theories., Comment: 7 pages, 5 figures, published version

We show that a nanopore in a silicon membrane connected to a voltage source can be used as an electrically tunable ion filter. By applying a voltage between the heavily doped semiconductor and the electrolyte, it is possible to invert the ion population inside the nanopore and vary the conductance for both cations and anions in order to achieve selective conduction of ions even in the presence of significant surface charges in the membrane. Our model based on the solution of the Poisson equation and linear transport theory indicates that in narrow nanopores substantial gain can be achieved by controlling electrically the width of the charge double layer.

We consider the finite-size corrections in the Dicke model and determine the scaling exponents at the critical point for several quantities such as the ground state energy or the gap. Therefore, we use the Holstein-Primakoff representation of the angular momentum and introduce a nonlinear transformation to diagonalize the Hamiltonian in the normal phase. As already observed in several systems, these corrections turn out to be singular at the transition point and thus lead to nontrivial exponents. We show that for the atomic observables, these exponents are the same as in the Lipkin-Meshkov-Glick model, in agreement with numerical results. We also investigate the behavior of the order parameter related to the radiation mode and show that it is driven by the same scaling variable as the atomic one., Comment: 4 pages, published version

We compute the quantum diffusion of electron wavepackets in two- and three-dimensional quasiperiodic structures: the generalized Rauzy tilings. The algorithm allows us to treat systems of more than one million sites, and to consider energy-filtered wavepackets. We show that the anomalous diffusion exponent, β , depends on the energy, and that the propagation is almost ballistic at band edges ( β ≃1). This study is completed by exact diagonalizations of small clusters. The results strongly suggest that band-edge eigenstates are extended, which is consistent with their ballistic propagation.

International audience

Metastable CuNbN2 is synthesized by a solid state ion-exchange reaction between polycrystalline NaNbN2 (obtained by solid state reaction of Na metal and NbN under ammonia flow at 500 °C for 24 h) and a 5-fold excess of CuI (N2 atmosphere, 300 °C, 48 h).

We consider the string-net model on the honeycomb lattice for Ising anyons in the presence of a string tension. This competing term induces a nontrivial dynamics of the non-Abelian anyonic quasiparticles and may lead to a breakdown of the topological phase. Using high-order series expansions and exact diagonalizations, we determine the robustness of this doubled Ising phase which is found to be separated from two gapped phases. An effective quantum dimer model emerges in the large tension limit giving rise to two different translation symmetry-broken phases. Consequently, we obtain four transition points, two of which are associated with first-order transitions whereas the two others are found to be continuous and provide examples of recently proposed Bose condensation for anyons., 10 pages, 8 figures, typos corrected

International audience; III-V/Si heterostructures are currently investigated for silicon photonics and solar energy conversion. In particular, dilute nitride alloy GaAsPN grown on a GaP/Si platform exhibits lattice match with Si and an optimal band gap configuration for tandem solar cell devices. However, monolithic "coherent" growth of the GaP thin layer on Si suffers from the nucleation of extended structural defects, which can hamper device operation as well as the GaP/Si interface level and through their propagation inside the overall heterostructure. However, the effect of such structural defects on optical and transport properties is actually not well understood in details. In this letter, we investigate the anti phase domains defect (also called inversion domains) by means of ab initio calculations giving insights into the alteration of optical and transport properties of GaP due to the defective GaP/Si interface.

We study a new class of quasiperiodic codimension one tilings based on a natural generalization of the Fibonacci chain. These so-called generalized Rauzy tilings allow for simple and explicit expressions of the site coordinates, and their associated tight-binding Hamiltonians are quickly written as band (Toeplitz-like) matrices. First results are given for their electronic properties which display similar behaviors as higher codimension tilings.

We propose a class of exactly solvable anisotropic tight-binding models on an infinite-dimensional hypercube. The energy spectrum is analytically computed and is shown to be fractal and/or absolutely continuous according to the value hopping parameters. In both cases, the spectral and diffusion exponents are derived. The main result is that, even if the spectrum is absolutely continuous, the diffusion exponent for the wave packet may be anything between 0 and 1 depending upon the class of models., Comment: 5 pages Latex

We present an extreme localization mechanism induced by a magnetic field for tight-binding electrons in two-dimensional structures. This spectacular phenomenon is investigated for a large class of tilings (periodic, quasiperiodic, or random). We are led to introduce the Aharonov-Bohm cages defined as the set of sites eventually visited by a wavepacket that can, for particular values of the magnetic flux, be bounded. We finally discuss the quantum dynamics which exhibits an original pulsating behaviour., 4 pages Latex, 3 eps figures, 1 ps figure

Recent revisions of defect formation energy calculations based on bandgap corrected hybrid functionals have raised concerns about the validity of earlier results based on standard density functionals and about the reliability of the theoretical prediction of electrical properties in semiconductor materials in general. We show here that a close agreement between the two types of functionals can be achieved by determining appropriate values for the electronic and atomic reference energies, thereby mitigating uncertainties associated with the choice of the underlying functional.

We examine the zero-temperature phase diagram of the two-dimensional Levin-Wen string-net model with Fibonacci anyons in the presence of competing interactions. Combining high-order series expansions around three exactly solvable points and exact diagonalizations, we find that the non-Abelian doubled Fibonacci topological phase is separated from two nontopological phases by different second-order quantum critical points, the positions of which are computed accurately. These trivial phases are separated by a first-order transition occurring at a fourth exactly solvable point where the ground-state manifold is infinitely many degenerate. The evaluation of critical exponents suggests unusual universality classes., 7 pages, 4 figures, published version