Spin-orbit torques and magnetization switching in (Bi,Sb)2Te3/Fe3GeTe2 heterostructures grown by molecular beam epitaxy

Topological insulators (TIs) hold promise for manipulating the magnetization of a ferromagnet (FM) through the spin-orbit torque (SOT) mechanism. However, integrating TIs with conventional FMs often leads to significant device-to-device variations and a broad distribution of SOT magnitudes. In this work, we present a scalable approach to grow a full van der Waals FM/TI heterostructure by molecular beam epitaxy, combining the charge-compensated TI (Bi,Sb)2Te3 with 2D FM Fe3GeTe2 (FGT). Harmonic magnetotransport measurements reveal that the SOT efficiency exhibits a non-monotonic temperature dependence and experiences a substantial enhancement with a reduction of the FGT thickness to 2 monolayers. Our study further demonstrates that the magnetization of ultrathin FGT films can be switched with a current density of Jc ∼ 1010 A/m2, with minimal device-to-device variations compared to previous investigations involving traditional FMs.This research has received funding from the European Union’s Horizon 2020 (EU H2020) research and innovation programme under grant agreement 881603 (Graphene Flagship) and was supported by the FLAG-ERA grant MNEMOSYN. ICN2 acknowledges support from the Spanish Ministry of Science and Innovation (MCIN) and Spanish Research Agency (AEI/10.13039/501100011033) under contracts PID2019-111773RB-I00, PCI2021-122035-2A, PID2022-143162OB-I00 (including FEDER funds), and Severo Ochoa CEX2021-001214-S. SPINTEC acknowledges support from the French ANR under contracts ANR-21-GRF1-0005-01 and ANR-20-CE24-0015 (ELMAX). T.G. and R.G. acknowledge support from EU H2020 programme under the Marie Skłodowska-Curie Grant Agreement Nos. 754510 and 840588 (GRISOTO, Marie Sklodowska-Curie fellowship), respectively, and JFS from MCIN/AEI/10.13039/50110001103 under contract RYC2019-028368-I.With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001214-S).Peer reviewe

Light Curves and Colors of the Ejecta from Dimorphos after the DART Impact

On 26 September 2022 the Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, a satellite of the asteroid 65803 Didymos. Because it is a binary system, it is possible to determine how much the orbit of the satellite changed, as part of a test of what is necessary to deflect an asteroid that might threaten Earth with an impact. In nominal cases, pre-impact predictions of the orbital period reduction ranged from ~8.8 - 17.2 minutes. Here we report optical observations of Dimorphos before, during and after the impact, from a network of citizen science telescopes across the world. We find a maximum brightening of 2.29 $\pm$ 0.14 mag upon impact. Didymos fades back to its pre-impact brightness over the course of 23.7 $\pm$ 0.7 days. We estimate lower limits on the mass contained in the ejecta, which was 0.3 - 0.5% Dimorphos' mass depending on the dust size. We also observe a reddening of the ejecta upon impact.Comment: Accepted by Natur

Simultaneous Bright- and Dark-Field X-ray Microscopy at X-ray Free Electron Lasers

The structures, strain fields, and defect distributions in solid materials underlie the mechanical and physical properties across numerous applications. Many modern microstructural microscopy tools characterize crystal grains, domains and defects required to map lattice distortions or deformation, but are limited to studies of the (near) surface. Generally speaking, such tools cannot probe the structural dynamics in a way that is representative of bulk behavior. Synchrotron X-ray diffraction based imaging has long mapped the deeply embedded structural elements, and with enhanced resolution, Dark Field X-ray Microscopy (DFXM) can now map those features with the requisite nm-resolution. However, these techniques still suffer from the required integration times due to limitations from the source and optics. This work extends DFXM to X-ray free electron lasers, showing how the $10^{12}$ photons per pulse available at these sources offer structural characterization down to 100 fs resolution (orders of magnitude faster than current synchrotron images). We introduce the XFEL DFXM setup with simultaneous bright field microscopy to probe density changes within the same volume. This work presents a comprehensive guide to the multi-modal ultrafast high-resolution X-ray microscope that we constructed and tested at two XFELs, and shows initial data demonstrating two timing strategies to study associated reversible or irreversible lattice dynamics

Augmentation de l'incidence apparente des pathologies thyroïdiennes depuis 1986 en France (poids relatifs de l'amélioration des moyens diagnostiques et des conséquences de Tchernobyl)

BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF

Microbolometer on polymer membrane with heat feedback control for non radiative applications

International audienc

BERTEPro : Une nouvelle approche de représentation sémantique dans le domaine de l'éducation et de la formation professionnelle

International audienceFlauBERT et CamemBERT ont établi une nouvelle performance de pointe pour la compréhension de la langue française. Récemment, SBERT a transformé l’utilisation de BERT, afin de réduire l’effort de calcul des encastrements de phrases, tout en maintenant la précision de BERT. Cependant, ces modèles ont été entraînés sur des textes non spécifiques de la langue française, ce qui ne permet pas une représentation fine des textes de domaines spécifiques, comme le domaine de l’éducation et de la formation professionnelle. Dans cet article, nous présentons BERTEPro, un modèle basé sur FlauBERT, dont l’apprentissage a été étendu sur des textes du domaine de l’éducation et de la formation professionnelle, avant d’être affiné sur des tâches NLI et STS. L’évaluation des performances de BERTEPro sur des tâches STS, ainsi que sur des tâches de classification, ont confirmé que la méthodologie proposée bénéficie d’avantages significatifs par rapport aux autres méthodes de l’état de l’art

BERTEPro : Une nouvelle approche de représentation sémantique dans le domaine de l'éducation et de la formation professionnelle

International audienceFlauBERT et CamemBERT ont établi une nouvelle performance de pointe pour la compréhension de la langue française. Récemment, SBERT a transformé l’utilisation de BERT, afin de réduire l’effort de calcul des encastrements de phrases, tout en maintenant la précision de BERT. Cependant, ces modèles ont été entraînés sur des textes non spécifiques de la langue française, ce qui ne permet pas une représentation fine des textes de domaines spécifiques, comme le domaine de l’éducation et de la formation professionnelle. Dans cet article, nous présentons BERTEPro, un modèle basé sur FlauBERT, dont l’apprentissage a été étendu sur des textes du domaine de l’éducation et de la formation professionnelle, avant d’être affiné sur des tâches NLI et STS. L’évaluation des performances de BERTEPro sur des tâches STS, ainsi que sur des tâches de classification, ont confirmé que la méthodologie proposée bénéficie d’avantages significatifs par rapport aux autres méthodes de l’état de l’art

A new sentence embedding framework for the education and professional training domain with application to hierarchical multi-label text classification

International audienceIn recent years, Natural Language Processing (NLP) has made significant advances through advanced general language embeddings, allowing breakthroughs in NLP tasks such as semantic similarity and text classification. However, complexity increases with hierarchical multi-label classification (HMC), where a single entity can belong to several hierarchically organized classes. In such complex situations, applied on specific-domain texts, such as the Education and professional training domain, general language embedding models often inadequately represent the unique terminologies and contextual nuances of a specialized domain. To tackle this problem, we present HMCCCProbT, a novel hierarchical multi-label text classification approach. This innovative framework chains multiple classifiers, where each individual classifier is built using a novel sentence-embedding method BERTEPro based on existing Transformer models, whose pre-training has been extended on education and professional training texts, before being fine-tuned on several NLP tasks. Each individual classifier is responsible for the predictions of a given hierarchical level and propagates local probability predictions augmented with the input feature vectors to the classifier in charge of the subsequent level. HMCCCProbT tackles issues of model scalability and semantic interpretation, offering a powerful solution to the challenges of domain-specific hierarchical multi-label classification. Experiments over three domain-specific textual HMC datasets indicate the effectiveness of HMCCCProbT to compare favorably to state-of-the-art HMC algorithms in terms of classification accuracy and also the ability of BERTEPro to obtain better probability predictions, well suited to HMCCCProbT, than three other vector representation techniques

Reinforcement learning application scenario for Opportunistic Spectrum Access

4 pagesInternational audienceWe tackle in this work a concrete scenario that illustrates the behavior of Cognitive Radio equipment within an Opportunistic Spectrum Access context. We assume that there exist two sets of users. On the one hand Primary Users who own the spectrum pool of interest. And one the other hand, Secondary Users who aim at exploiting vacant communication opportunities left by Primary Users at a given time in a given band. Moreover, Secondary Users are assumed to have no a priori knowledge on Primary Users behavior and aim at learning missing information while exploiting found communication opportunities. For that purpose, we model Primary Users' frequency bands occupations pattern using an OFDM modulation. While, the introduced secondary user's learning process relies on an energy detector and a reinforcement learning algorithm known as UCB1. The complete model is developed on Simulink to illustrate the behavior of the Primary Network as well as the Secondary User