Boron vacancies in hexagonal boron nitride (hBN) are among the most extensively studied optically active spin defects in van der Waals crystals, due to their promising potential to develop two-dimensional (2D) quantum sensors. In this letter, we demonstrate the tunability of the charge state of boron vacancies in ultrathin hBN layers, revealing a transition from the optically active singly negatively charged state to the optically inactive doubly negatively charged state when sandwiched between graphene electrodes. Notably, there is a photoluminescence quenching of a few percent upon the application of a bias voltage between the electrodes. Our findings emphasize the critical importance of considering the charge state of optically active defects in 2D materials, while also showing that the negatively charged boron vacancy remains robust against external perpendicular electric fields. This stability makes it a promising candidate for integration into various van der Waals heterostructures.

While island biogeography focuses on species richness equilibrium driven by immigration and extinction, and metapopulation theory examines single-species dynamics across fragmented habitats, their interplay remains poorly understood. In particular, the species-area relationship remains a subject of ongoing debate, yet there are limited theoretical foundations to explain it. To address this, we developed a multiscale stochastic metapopulation model to investigate diversity patterns on islands, bridging the gap between island biogeography and metapopulation theory. Our model integrates regional colonization from a mainland with local colonization-extinction processes within islands at the single-species level, then extends this to multiple, independent species. By analyzing the stationary properties of this model, we generate novel predictions of Species Area Relationship (SAR) based on local extinction rates, within-island colonization rates, and mainland immigration rates. We demonstrate how the interplay of these parameters influences the relationship, predicting patterns that can resemble either the power-law of Arrhenius or the semi-logarithmic relationship of Gleason, depending on the relative importance of mainland immigration versus within-island dynamics, and on the nature of the species abundance distribution in the mainland. This unified framework offers new insights into the mechanisms driving species richness and distribution across spatial scales, providing a more holistic understanding of biodiversity patterns in fragmented landscapes.

We discuss recent improvements of the cold and dense QCD pressure owing to an all-order resummation of the soft modes, or to the so-called renormalization group optimized perturbation theory (RGOPT). Both approaches show a significant improvement of the residual renormalization scale dependence with respect to the state-of-the-art results for the perturbative pressure.

We investigate the effect of confinement on the magnetic state of a 12−n⁢m-thick Fe₅GeTe₂ layer grown by molecular beam epitaxy. We use quantitative scanning nitrogen-vacancy magnetometry to locally extract the magnetization in rectangular uniformly in-plane magnetized microstructures, showing no enhancement of the Curie temperature compared to magnetization measurements performed before patterning the film, in contrast to previous results obtained on thick Fe₃GeTe₂ flakes. Under the application of a weak out-of-plane magnetic field, we observe the stabilization of magnetic vortices at room temperature in micrometric squares. Finally, we highlight the effect of the size of the patterned microdisks and microsquares on the stabilization of the vortices using experiments and micromagnetic simulations. Our work thus proposes and demonstrates a way to stabilize noncollinear textures at room temperature in a van der Waals magnet using confinement.

The quantum spin Hall effect (QSHE), a hallmark of topological insulators, enables dissipationless, spin-polarized edge transport and has been predicted in various two-dimensional materials. However, challenges such as limited scalability, low-temperature operation, and the lack of robust electronic transport have hindered practical implementations. Here, we demonstrate the QSHE in an InAs/GaInSb/InAs trilayer quantum well structure operating at elevated temperatures. This platform meets key criteria for device integration, including scalability, reproducibility, and tunability via electric field. When the Fermi level is positioned within the energy gap, we observe quantized resistance values independent of device length and in both local and nonlocal measurement configurations, confirming the QSHE. Helical edge transport remains stable up to T = 60 kelvin, with further potential for higher-temperature operation. Our findings establish the InAs/GaInSb system as a promising candidate for integration into next-generation devices harnessing topological functionalities, advancing the development of topological electronics.

Carbon nanotube are exceptional mechanical resonators. Indeed, they are extremely light, with masses in the range of ~ag (1 ag = 10-18g). In addition, as bottom-up materials, they do not suffer from surface defect as their top-down counterparts (MEMS etched from silicon or nitride substrates). From these 2 features stems their exquisite mass sensitivity as demonstrated by Chaste et al[1] with a sensitivity of 1.4 yg in a cryogenic environment. Yet, this sensitivity was reported to be much worse at room temperature, about 25 zg[2]. This has hindered the use of CNTs as sensors in real-life applications. In this work, we propose a unique set-up to track in real time the vibrations of a individual single-walled CNT (SWCNTs) at room temperature. It allows us to demonstrate a record mass sensitivity of 0.2 yg +/- 0.17 yg (1 yg = 10-24 g, the mass of a single proton).We carefully investigated the noise mechanisms that could be limiting the sensitivity: set-up noise, interaction with the gas phase and Brownian motion to name only the most important ones. We found that our device operates closely to the Brownian noise limit and is not limited by external sources of noise. Surprisingly, increasing the pressure up to 35 mbar (after which we could not detect the motion due to viscous damping) does not seem to degrade the sensitivity, which might be preserved up to ambient pressure. Finally, yet importantly, the exquisite sensitivity observed here is similar for several devices, making it a reliable and reproducible feature. This opens up the possibility to perform single-molecule sensing, in various contexts such as biological applications, mass spectrometry or surface science[1,3].[1] J. Chaste, A. Eichler, J. Moser, G. Ceballos, R. Rurali, A. Bachtold (2012). A nanomechanical mass sensor with yoctogram resolution, Nat. Nano, 7, 5, 301-304.[2] B. Lassagne, D. Garcia-Sanchez, A. Aguasca, A. Bachtold (2008). Ultrasensitive mass sensing with a nanotube electromechanical resonator, Nano. Let., 8, 11, 3735 – 3738.[3] P. Robin, L. Bocquet (2023). Nanofluidics at the crossroads, Soft Cond. Matt., preprint.