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International audience; In this article, I analyse the functioning of convertible local currencies (CLC) through the economic base theory. I thereby highlight CLC' mechanisms that can contribute to the development of the territorial economy, in particular the internalisation of their members' demand inside their communities. Indeed, CLCs might impact the circulation of income within the local economy by limiting the outflow of income from the territory and increasing its circulation within the domestic sector. CLCs therefore fit more specifically into consumer base theory, which promotes endogenous territorial development by directing local demand towards local production. However, CLCs users gather only a fraction of local actors, their members having to choose to join and, for companies, to be certified by the managing organisations. CLCs therefore only support the development of specific communities, who share similar values and practices, but whose growth can transform territorial economies.Nevertheless, in order for the demand internalisation to really benefit the economic development of their sub-territorial community, it is necessary to determine whether it really irrigates productive activities and not only distribution ones. To investigate which part of the economy is mostly supported by the internalisation of the users’ demand, I analyse the digital transaction data from the SoNantes and the Eusko, two French CLCs. The two CLCs are essentially implanted in the domestic sectors. If the SoNantes integrates more companies dedicated to productive activities support than the Eusko, the two CLCs mainly irrigate activities geared towards distribution and household consumption. The circulation of income from these sectors to productive activities remains low, limiting their economic development support potential.; Dans cet article, nous analysons le fonctionnement des monnaies locales convertibles (MLC) au travers de la théorie de la base économique. Nous mettons ainsi en évidence les mécanismes des MLC pouvant favoriser le développement de l’économie territoriale, notamment l’internalisation de la demande de leurs membres. Les utilisateurs des MLC ne représentent qu’une fraction des acteurs du territoire. Les MLC soutiennent donc le développement de sous-communautés spécifiques, mais dont la croissance peut transformer les économies territoriales. L’analyse des données de transaction numérique de la SoNantes et l’Eusko dévoile les sphères économiques empiriquement soutenues par les MLC. Ainsi, ces deux MLC françaises s’implantent essentiellement dans les secteurs domestiques et si, la SoNantes intègre des entreprises dédiées au soutien à des activités productives, les deux MLC irriguent majoritairement des activités de distribution et de consommation courante à destination des ménages. La transmission des recettes perçues par ces secteurs à des activités productives demeure faible, limitant le réel potentiel de développement économique des MLC.

International audience; This article analyses how convertible local currencies (CLCs) contribute to their circulating territory, in the case of France, where a systematic survey was held in 2019–20. It builds a framework in which CLCs contribute to a territorialized infrastructure and assume functions of territorial intermediation, thus supporting a territorial development process. It examines how the CLC organizations define their territory, before assessing the territorial development they carry, with evidence about their size, role in the territorial coordination of actors and governance issues. This assessment raises doubts about their actual contribution to territorial development, while possible achievements are discussed.

International audience; In this article, we investigate the role played by a local currency in the construction of organised proximities between local businesses. By defining the local currency as an intermediation operator, we specify the roles played by this device among the economic actors who join it. The article is based on an analysis of the durability and intensity of business-to-business relationships in local currency and the meaning that actors give to these relationships. The study of quantitative and qualitative data from the case of the eusko in the Basque Country shows that the currency fulfils several intermediation functions that generate norms, values, practices and representations shared by the actors, giving them the feeling of being close. The circulation of money pushes some firms to look for new local partners in order to reuse the local money they receive from their customers. This incentive has contrasting effects depending on the business sector, but the analysis suggests that beyond commercial links, participation in the monetary community produces specific relationships between businesses. Indeed, the use of the local currency generates, over the course of exchanges, specific practices and shared meanings in professional relationships. As a matter of fact, businesses have a variety of uses for the local currency, including business-to-business trade but also solidarity practices. By creating distinctive practices within its users community, the local currency generates organised proximities. The analysis of the uses of the local currency by the entrepreneurs also reveals the centrality of a moral dimension in the construction of these forms of proximity.; L’article examine le rôle joué par une monnaie locale dans la construction de proximités organisées entre entreprises d’un même territoire. En définissant la monnaie locale comme un opérateur d’intermédiation, l’article s’attache à préciser les rôles joués par ce dispositif auprès des acteurs économiques qui s’y enrôlent. L’étude de données quantitatives et qualitatives issues du cas de l’eusko au Pays Basque montrent que la monnaie remplit plusieurs fonctions d’intermédiation qui génèrent de la proximité en activant des logiques d’appartenance et de similitude parmi les acteurs économiques engagés. L’analyse des usages de la monnaie locale par les entrepreneurs révèle en outre la centralité d’une dimension morale dans la construction de ces formes de proximité.

This thesis focuses on the effects of the circulation of French convertible local currencies (CLCs) on their users exchange networks, the organization of their commercial transactions and the development of their economic activity. It proposes a theoretical advance by conceiving CLCs and their socio-economic impacts in a unified perspective within the framework of regional economy, in particular through the concepts of territorial intermediation, organized proximities and local multiplier. This initial conceptualization structures a mostly quantitative empirical research presented in three chapters and mobilizing multiple sources (quantitative survey, transaction data, administrative data) associated with adapted analysis methods (descriptive, network analysis, econometrics on panel data, mixed methods).It thus highlights the role of territorial intermediation played by CLCs and through which they contribute to the activation of proximities within their monetary community, as well as to the development of trade relations between their users. This process favors the circulation of income within the community of users and leads to multipliers internal to the CLCs that are slightly higher than the local multipliers usually measured. This results in a positive effect on the turnover of member companies of around 10% to 15% according to our estimates, particularly for micro-enterprises and small and medium-sized enterprises.; Cette thèse porte sur les effets de la circulation des monnaies locales convertibles (MLC) françaises sur les réseaux d’échange de leurs utilisateurs, l’organisation de leurs transactions commerciales et le développement de leur activité économique. Elle propose une avancée théorique en pensant les MLC et leurs effets socioéconomiques de façon unifiée au sein du cadre d’analyse de l’économie territoriale, notamment au travers des concepts d’intermédiation territoriale, de proximités organisées et de multiplicateur local. Cette conceptualisation initiale structure un travail empirique essentiellement quantitatif présenté en trois chapitres et mobilisant des sources multiples (enquête quantitative, données de transactions, données administratives) associées à des méthodes d’analyse adaptées (descriptive, analyse de réseau, économétrie sur données de panel, méthodes mixtes).Elle met ainsi en évidence le rôle d’intermédiation territoriale endossé par les MLC et par lequel elles participent à l’activation de proximités au sein de leur communauté monétaire, ainsi qu’à la génération de relations commerciales entre leurs utilisateurs. Ce processus favorise la circulation des revenus au sein de la communauté d’utilisateurs et résulte en des multiplicateurs internes aux MLC légèrement supérieurs aux multiplicateurs locaux habituellement mesurés. Il en découle un effet positif sur les chiffres d’affaires des entreprises adhérentes de l’ordre de 10% à 15% selon nos estimations, et particulièrement pour les microentreprises et petites et moyennes entreprises.

This article will investigate the links between convertible local currencies (CLCs) and economic localisation. Following on the qualitative study by Marshall and O'Neil (2018), we will answer the following question: to what extent do convertible local currencies foster the localisation of procurement and production by creating new commercial relationships between businesses that use them?We will use data from a quantitative survey conducted by the Mouvement SOL, a French net- work of CLCs, for individual (n=1597) and provider (n=542) users of French CLCs. We will also address how new providers are found through the currency and analyse the change in con- sumption and production practices. This first analysis will be supported by a case study on the Eusko, the largest convertible local currency in France. The Eusko case makes it possible to cross-reference the survey data from Eusko users with the transaction data from digital Eusko users in order to evaluate whether the results of forming commercial relationships between companies are consistent across both sources. We will also use digital Eusko transaction data to run a network analysis, enabling us to observe the development of commercial relationships inside the community over time. We found that between one fourth to one third of businesses in a CLC network find new business partners in their CLC community, connecting with 3.5 new partners on average. These results are more encouraging than the absence of localisation found by Marshall and O’Neil (2018).Transaction data also allows us to determine which sectors benefit the most from the circulation of CLC and thus draw a conclusion on the capacity of the currency to move from the localisation of procurement to the localisation of production. Our results on this point are more balanced. The retail sector benefits the most from the circulation of Eusko and actors in this sector ex- change 40% of the CLC received into national currency, limiting the flow of income exchanged within the CLC.

Convertible local currencies are alternative monetary instruments issued by groups of citizens to circulate in a given territory. They are used by businesses and citizens who accept it as means of payments constituting, hence, a monetary community. Their impacts on economic activity are mainly related to their circulation within the user community. Businesses that have received local currency as payment must spend it with other members. A local currency, thus, acts as a constraint favoring the development of new commercial relations in the network and increasing the demand among local businesses involved in the scheme. In this article, we model the income circulation between convertible currencies users as a local multiplier, called the convertible local currency multiplier. By using the Local Multiplier 3 empirical approach (Sacks, 2002) on two convertible currencies transactions data, we compute an indicator summarizing the income generated for the monetary community by the change and expense of euros into a local currency. This new indicator enables not only consumers to estimate the impact of their actual consumption in local currency, but also potential public decision-makers to know the total effect of their expenses when they use local currency on their territory to finance some of their policies. For example, this indicator could be used to measure the direct and indirect effects of a subsidy paid in local currency to institutions, businesses or households. The computed multiplier is greater than two for both currencies, which is in the higher range of LM3 estimated in the literature.

International audience

International audience

This national survey on local currencies in France was conducted online between November, 2019 and January, 2020. 63 associations that already circulated their local currency filled the questionnaire, on an estimated number of 82 circulating local currencies as of end 2019. This report analyses the data from this survey. After some methodological considerations, it studies the characteristics of the issuing associations, the characteristics of the issued currencies, the monetary activity of the associations and the links between them and the socio-economic actors of the territory.; Cette enquête nationale sur les monnaies locales en France a été administrée en ligne de novembre 2019 à janvier 2020. 63 associations ayant mis en circulation une monnaie locale ont répondu à l’enquête, sur un nombre estimé de 82 monnaies locales en circulation à la fin 2019. Ce rapport traite les données issues de cette enquête : après quelques repères méthodologiques, il étudie les caractéristiques des associations émettrices, les caractéristiques des monnaies émises, l'activité monétaire des associations et les liens des associations avec les acteurs socio-économiques du territoire.

Heavy alkali-metal treatment of Cu(In,Ga)Se2 (CIGSe) absorbers has been emerging as a key process for achieving over 23% high conversion efficiencies in CIGSe solar cells. Here, we investigate the effect of rubidium fluoride post-deposition treatment (RbF-PDT) on the electronic and carrier recombination properties of narrow bandgap (narrowgap) gap and wide bandgap (widegap) CIGSe solar cells using thermal admittance spectroscopy (TAS), transient photocapacitance spectroscopy (TPC), as well as time-resolved photoluminescence (TRPL). We find that the activation energy of the main capacitance step in TAS spectra of narrowgap and widegap CIGSe solar cells reduces after RbF-PDT. On the other hand, capacitance–voltage (C–V) and temperature-dependent current–voltage (IVT) measurements demonstrate that the built-in potential, as well as the activation energy Ea, increases upon RbF-PDT both for narrowgap and widegap samples, pointing to reduced interface recombination. TPC revealed an appreciable reduction of the optical response of bulk defects in the narrowgap and widegap CIGSe, suggesting improvement of bulk properties after RbF treatment. TRPL confirmed that RbF-PDT significantly reduces carrier recombination in the bulk of narrowgap and widegap CIGSe absorbers and at the surface, leading to extended carrier lifetimes. Analysis of open-circuit voltage ( V O C ) losses due to nonradiative recombination in the bulk of the CIGSe showed a strong correlation between enhanced carrier lifetime and improved V O C for narrow gap CIGSe cells. In contrast, although we observed a substantial decrease of V O C losses in widegap CIGSe bulk, the analysis indicated that the key to photovoltaic performance enhancement is improved interface quality.

International audience; We study the emission of individual quantum dots in CdTe/ZnTe samples doped with a low concentration of Cr. In addition to dots with a photoluminescence (PL) split by the exchange interaction with a magnetic Cr atom, we observe another type of dots with a complex PL structure composed of a minimum of six lines on the exciton and biexciton and three lines on the charged excitons. In these dots, the linear polarization dependence and the magnetic field dependence of the PL behave like three similar quantum dots emitting at slightly different energies. Cross-correlation intensity measurements show that these emission lines are not independent but exchange intensities in a time scale of a few hundred nanoseconds depending on the optical excitation power. We attribute this PL structure to charge fluctuations of a Cr atom located in the vicinity the CdTe dots in the ZnTe barrier. We present a model which confirms that the presence of a single charge fluctuating between-e (Cr +), 0 (Cr 2+) and +e (Cr 3+) and located a few nm away from the dot explains the observation of three emission energies. We finally show that the interaction between the confined carriers and the nearby fluctuating localized charge can be modified by an applied static electric field which modulates the splitting of the emission lines.

We demonstrate that the spin of a Cr atom in a quantum dot (QD) can be controlled optically and we discuss the main properties of this single spin system. The photoluminescence of individual Cr-doped QDs and their evolution in magnetic field reveal a large magnetic anisotropy of the Cr spin induced by local strain. This results in a splitting of the Cr spin states and in a thermalization on the lower energy states states S$_z$=0 and S$_z$=$\pm$1. The magneto-optical properties of Cr-doped QDs can be modelled by an effective spin Hamiltonian including the spin to strain coupling and the influence of the QD symmetry. We also show that a single Cr spin can be prepared by resonant optical pumping. Monitoring the intensity of the resonant fluorescence of the QD during this process permits to probe the dynamics of the optical initialization of the spin. Hole-Cr flip-flops induced by an interplay of the hole-Cr exchange interaction and the coupling with acoustic phonons are the main source of relaxation that explains the efficient resonant optical pumping. The Cr spin relaxation time is measured in the $\mu s$ range. We evidence that a Cr spin couples to non-equilibrium acoustic phonons generated during the optical excitation inside or near the QD). Finally we show that the energy of any spin state of an individual Cr atom can be independently tuned by a resonant single mode laser through the optical Stark effect. All these properties make Cr-doped QDs very promising for the development of hybrid spin-mechanical systems where a coherent mechanical driving of an individual spin in an oscillator is required., Comment: arXiv admin note: text overlap with arXiv:1606.04221, arXiv:1609.08829

A detailed analysis of the photoluminescence (PL) intensity distribution in singly Cr-doped CdTe/ZnTe quantum dots (QDs) is performed. First of all, we demonstrate that hole-Cr flip-flops induced by an interplay of the hole-Cr exchange interaction and the coupling with acoustic phonons are the main source of spin relaxation within the exciton-Cr complex. This spin flip mechanism appears in the excitation power dependence of the PL of the exciton as well as in the intensity distribution of the resonant PL. The resonant optical pumping of the Cr spin which was recently demonstrated can also be explained by these hole-Cr flip-flops. Despite the fast exciton-Cr spin dynamics, an analysis of the PL intensity under magnetic field shows that the hole-Cr exchange interaction in CdTe/ZnTe QDs is antiferromagnetic. In addition to the Cr spin dynamics induced by the interaction with carriers' spin, we finally demonstrate using time resolved optical pumping measurements that a Cr spin interacts with nonequilibrium acoustic phonons generated during the optical excitation inside or near the QD.

Two different single spin systems are studied in this thesis: single Mn spin in positively charged quantum dots, and single Cr atom in a neutral quantum dots. Both are probed optically, using the photoluminescence of a single dot. Both systems are strongly coupled to phonons and strains. This coupling opens new ways to probe and control the spins of the magnetic atoms, not only optically, but also by modulating the strain state at their position.Using resonant photoluminescence, we demonstrate the existence of optical Λ-level systems in Mn-doped positively charged quantum dots, and use them to study the dynamics of the hole-Mn hybrid spin. It reveals hole-Mn spin flip-flops in the nanosecond range due to the interplay of the interaction with acoustic phonons and the hole-Mn exchange interaction. We also show that degenerated electron-Mn states separated by spin flips of two units are coupled through the in-plane strain anisotropy, and study this strain induced coherent dynamics.Using magneto-optic experiments, we are able to probe the spin of a single Cr atom and extract a magnetic anisotropy D0 in the meV range. Several parameters of the QD are extracted from these experiments, and, especially, we show that the h-Cr coupling is anti-ferromagnetic. We demonstrate that the Cr spin can be prepared using resonant optical pumping. These experiments evidence a Cr relaxation time under excitation in the 10 nanoseconds range. This relaxation is driven by hole-Cr spin flip-flops caused by the interplay of the interaction with acoustic phonons and the hole-Cr exchange interaction. A relaxation in the dark in the microseconds range was also measured. Possibility of control of the Cr spin was also demonstrated using the optical Stark effect., Deux systèmes de spins uniques sont étudiés dans cette thèse : d’abord un unique atome de Mn dans une boîte quantique chargée positivement, puis un unique atome de Cr dans une boîte quantique neutre. Cette étude a été entièrement réalisée par des moyens optiques, via la photoluminescence d’une boîte unique. Ces deux systèmes sont fortement couplés aux phonons et aux contraintes. Ce couplage permet de ne plus se limiter à une détection et une manipulation du spin optique, mais ouvre également la possibilité de le faire en modulant le champ de contrainte.Par des expériences de photoluminescence résonante, nous montrons l’existence de niveaux optique en Λ dans les boîtes quantiques chargées positivement et dopées d’un unique atome de Mn. Ces niveaux en Λ sont utilisés pour étudier la dynamique du spin hybride trou-Mn. Cette étude révèle l’existence de flip-flops des spins du trou et du Mn à l’échelle de la nanoseconde, dus à l’interaction d’échange trou-Mn et à l’interaction avec les phonons acoustiques. Un couplage par l’anisotropie des contraintes dans le plan de niveaux électron-Mn dégénérés et séparé par un spin flip de deux unités est aussi démontré, et dynamique cohérente induite par les contraintes est étudiée en détail.Grâce à des expériences magnéto-optiques, nous avons pu détecter la photoluminescence d’un atome de Cr unique dans une boîte quantique, et extraire une anisotropie magnétique du spin du Cr de quelques meV. De nombreux paramètres des boîtes étudiées peuvent être extrait de ces expériences, et nous montrons notamment que le couplage trou-Cr est antiferromagnétique. Nous démontrons que le spin du Cr peut être préparé par pompage optique résonant. Ces expériences ont permis de montrer que, sous excitation, le spin du Cr fait des flip-flops avec celui du trou, causé par l’interaction d’échange trou-Cr et le couplage aux phonons acoustiques. Ces flip-flops causent une relaxation rapide du spin du Cr sous excitation, mesurée comme de l’ordre de quelques dizaines de nanosecondes. Dans le noir, nous avons trouvé que le spin du Cr relaxe en quelques microsecondes. Finalement, nous avons aussi démontré la possibilité de contrôler le spin du Cr par l’effet Stark optique.

International audience; We analyze, through resonant photoluminescence, the spin dynamics of an individual magnetic atom (Mn) coupled to a hole in a semiconductor quantum dot. The hybrid Mn hole spin and the positively charged exciton in a CdTe/ZnTe quantum dot form an ensemble of Λ systems which can be addressed optically. Autocorrelation of the resonant photoluminescence and resonant optical pumping experiments are used to study the spin relaxation channels in this multilevel spin system. We identified for the hybrid Mn hole spin an efficient relaxation channel driven by the interplay of the Mn hole exchange interaction and the coupling to acoustic phonons. We also show that the optical Λ systems are connected through inefficient spin flips than can be enhanced under weak transverse magnetic field. The dynamics of the resonant photoluminescence in a p-doped magnetic quantum dot is well described by a complete rate equation model. Our results suggest that long-lived hybrid Mn hole spin could be obtained in quantum dot systems with large heavy-hole/light-hole splitting.

International audience; A Cr atom in a semiconductor host carries a localized spin with an intrinsic large spin to strain coupling, which is particularly promising for the development of hybrid spin-mechanical systems and coherent mechanical spin driving. We demonstrate here that the spin of an individual Cr atom inserted in a semiconductor quantum dot can be controlled optically. We first show that a Cr spin can be prepared by resonant optical pumping. Monitoring the time dependence of the intensity of the resonant fluorescence of the quantum dot during this process permits us to probe the dynamics of the optical initialization of the Cr spin. Using this initialization and readout technique we measured a Cr spin relaxation time at T=5 K in the microsecond range. We finally demonstrate that, under a resonant single-mode laser field, the energy of any spin state of an individual Cr atom can be independently tuned by using the optical Stark effect.

English version of the paper.; In most countries, national statistical offices periodically run large surveys that provide outstanding insights on several subjects: social, economic, health, cultural, political. In many cases, this data is only used to produce nationally aggregated indicators that feed international statistical portals (WDGs, SDGs, World Bank, WHO, United Nations…). However, it is possible to do much more with the raw data collected during these surveys: calculate other indicators, cross different variables, run analysis for subnational areas, as well as more sophisticated analysis. This survey data is accessible to scholars, students, policy makers or practitioners and is most useful for the appraisal, monitoring and evaluation of development projects, programs and public policies. We first describe the typology of data generally available in developing countries, its possible uses and how to obtain it. Then we provide detailed guidelines on how to analyze it, using the survey package, available for R, a free and open source statistical software. We illustrate the step by step procedure for survey data processing using Democratic Republic of the Congo as an example: several surveys of different type and from different dates (MICS 2010, 1-2-3 2012 and DHS 2014) are analyzed to understand the levels and trends of access to drinking water, in particular in the Kinshasa megacity.; Les enquêtes menées périodiquement par les instituts nationaux de la statistique dans la plupart des pays du monde couvrent des thèmes très divers : sociaux, économiques, sanitaires, culturels et politiques. Sous-exploitées, ces enquêtes ne sont souvent traduites qu’en quelques grands indicateurs agrégées au niveau national, qui alimentent les portails statistiques internationaux (OMD/ODD, Banque mondiale, Organisation mondiale de la santé, Nations Unies…). Cette utilisation reste très limitée, en comparaison aux multiples calculs d’indicateurs, croisements de variables et périmètres d’analyse que permettent les données détaillées collectées lors de ces enquêtes. Ces bases de données brutes sont pourtant accessibles aux chercheurs, étudiants, décideurs ou praticiens et elles permettent par exemple d’éclairer la conception, le suivi et l’évaluation de projets, programmes et politiques publique. Après avoir décrit les utilisations possibles pour des interventions de développement, ce document décrit où et comment obtenir ces données et la manière de les analyser, grâce au package survey, disponible sur R, un logiciel statistique libre et gratuit. La démarche d’analyse est illustrée par l’exemple de la République Démocratique du Congo où des enquêtes de nature différentes (MICS 2010, 1-2-3 2012 et DHS2014) permettent de mieux comprendre les caractéristiques et l’évolution de l’accès à l’eau, enparticulier dans la mégalopole de Kinshasa.

We probe the spin dynamics of an individual magnetic atom (Mn) coupled to carriers in a positively charged quantum dot using resonant photoluminescence. We demonstrate that a p-doped CdTe/ZnTe quantum dot containing a single Mn atom forms an ensemble of optical Λ systems which can be addressed independently. Performing resonant optical pumping experiment and auto-correlation of the resonant photoluminescence, we show that these Λ systems are connected through inefficient forbidden spin-flips. We demonstrate that the spin dynamics of X+-Mn under resonant excitation is mainly controlled by the electron-Mn interaction. This coherent dynamics is directly observed in the time domain and is shown to be highly sensitive to the local strain at the Mn location. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

International audience; We demonstrate the optical addressability of the spin of an individual chromium atom (Cr) embedded in a semiconductor quantum dot. The emission of Cr-doped quantum dots and their evolution in magnetic field reveal a large magnetic anisotropy of the Cr spin induced by local strain. This results in the zero field splitting of the 0, ±1, and ±2 Cr spin states and in a thermalization on the magnetic ground states 0 and ±1. The observed strong spin to strain coupling of Cr is of particular interest for the development of hybrid spin-mechanical devices where coherent mechanical driving of an individual spin in an oscillator is needed. The magneto-optical properties of Cr-doped quantum dots are modeled by a spin Hamiltonian including the sensitivity of the Cr spin to the strain and the influence of the quantum dot symmetry on the carrier-Cr spin coupling.

We studied the spin dynamics of a Cr atom incorporated in a II-VI semiconductor quantum dot using photon correlation techniques. We used recently developed singly Cr-doped CdTe/ZnTe quantum dots (A. Lafuente-Sampietro {\it et al.}, [1]) to access the spin of an individual magnetic atom. Auto-correlation of the photons emitted by the quantum dot under continuous wave optical excitation reveals fluctuations of the localized spin with a timescale in the 10 ns range. Cross-correlation gives quantitative transfer time between Cr spin states. A calculation of the time dependence of the spin levels population in Cr-doped quantum dots shows that the observed spin dynamics is controlled by the exciton-Cr interaction. These measurements also provide a lower bound in the 20 ns range for the intrinsic Cr spin relaxation time.

We report on the coherent dynamics of the spin of an individual magnetic atom coupled to carriers in a semiconductor quantum dot which has been investigated by resonant photoluminescence of the positively charged exciton $({\mathrm{X}}^{+})$. We demonstrate that a positively charged CdTe/ZnTe quantum dot doped with a single Mn atom forms an ensemble of optical $\mathrm{\ensuremath{\Lambda}}$ systems which can be addressed independently. We show that the spin dynamics of the ${\mathrm{X}}^{+}$-Mn complex is dominated by the electron-Mn exchange interaction and report on the coherent dynamics of the electron-Mn spin system that is directly observed in the time domain. Quantum beats reflecting the coherent transfer of population between electron-Mn spin states, which are mixed by an anisotropic strain in the plane of the quantum dot, are clearly observed. We finally highlight that this strain-induced coherent coupling is tunable with an external magnetic field.

Gd${}_{1-x}$Tb${}_{x}$MnO${}_{3}$ oxides are characterized by two main competing states that exhibit both ferroelectric and multiferroic ordering. Both states involve cycloidal magnetic order that drives ferroelectricity. In their new article, a collaboration of researchers from Japan discovered that exposure of Gd${}_{0.5}$Tb${}_{0.5}$MnO${}_{3}$ to x-ray irradiation induces a reversible transition into a new hidden state, which is also characterized by cycloidal order, but with a different modulation wave vector. The ability to manipulate the state with x-rays suggests a novel route for photocontrol of multiferroic materials.