Communications Materials最新文献

Quantum light sources, particularly single-photon emitters (SPEs), are critical for quantum communications and computing. Among them, III-V semiconductor quantum dots (QDs) have demonstrated superior SPE metrics, including near-unity brightness, high photon purity, and indistinguishability, making them especially suitable for quantum applications. However, their overall quantum efficiency-determined by a product of the internal, excitation, and outcoupling efficiencies-remains limited, primarily due to low (typically below 0.1%) excitation efficiency. To mitigate the low efficiency under non-resonant pumping, here we realize liquid droplet etched GaAs QDs in a microscale 3D AlGaAs charge-carrier funnel. The funnel channels charge carriers to the QD and enhances the overall emission efficiency by over one order of magnitude while preserving the SPE behavior. We reveal that a modified energy landscape around the QD leads to the excitation efficiency improvement. These energy landscape-modified QDs can be operated with optical excitation up to 10 μm away, raising the promise of efficient electrically driven QD SPEs for quantum information systems.

Ultra-pure materials are highly valued as model systems for the study of intrinsic physics. Frequently, however, the crystal growth of such pristine samples requires significant optimization. PtSn₄ is a rare example of a material that naturally forms with a very low concentration of crystalline defects. Here, we investigate the origin of its low defect levels using a combination of electrical resistivity measurements, computational modeling, and scanning tunneling microscopy imaging. While typical flux-grown crystals of PtSn₄ can have residual resistivity ratios (RRRs) that exceed 1000, we show that even at the most extreme formation speeds, the RRR cannot be suppressed below 100. This aversion to defect formation extends to both the Pt and Sn sublattices, which contribute with equal weight to the conduction properties. Direct local imaging with scanning tunneling microscopy further substantiates the rarity of point defects, while the prohibitive energetic cost of forming a defect is demonstrated through density functional theory calculations. Taken together, our results establish PtSn₄ as an intrinsically defect-intolerant material, making it an ideal platform to study other properties of interest, including extreme magnetoresistance and topology.

Oxygen loss is a common defect type in perovskites which is caused by a low oxygen background pressure during growth. BaBiO_3-δ thin films are grown by molecular beam epitaxy on SrTiO₃-buffered Si(001) substrates. Although activated oxygen is supplied during growth, large amount of oxygen vacancies is created in the thin film depending on the cooldown process. Perovskite structure is obtained when the cooldown process includes an extended period during which activated oxygen is supplied. Another way for inducing the structural transformation is enabled via an ex-situ anneal at molecular oxygen. The transformation into BaBiO₃ is manifested as reconstructed octahedra based on transmission electron microscopy, Raman spectroscopy, and photoluminescence. Additionally, smaller out-of-plane lattice constant is observed for the perovskite phase supported by X-ray diffraction. Thermal mismatch and multivalency-facilitated tensile strain exerted on the layers by the underlying Si substrates are presented as the driving force behind the creation of oxygen vacancies.

Today, devices based on phase change materials (PCMs) are expanding beyond their traditional application in non-volatile memory, emerging as promising components for future neuromorphic computing systems. Despite this maturity, the electronic transport in the amorphous phase is still not fully understood, which holds in particular for the resistance drift. This phenomenon has been linked to physical aging of the glassy state. PCM glasses seem to evolve towards structures with increasing Peierls-like distortions. Here, we provide direct evidence for a link between Peierls-like distortions and local current densities in nanoscale phase change devices. This supports the idea of the evolution of these distortions as a source of resistance drift. Using a combination of density functional theory and non-equilibrium Green's function calculations, we show that electronic transport proceeds by states close to the Fermi level that extend over less distorted atomic environments. We further show that nanoconfinement of a PCM leads to a wealth of phenomena in the atomic and electronic structure as well as electronic transport, which can only be understood when interfaces to confining materials are included in the simulation. Our results therefore highlight the importance and prospects of atomistic-level interface design for the advancement of nanoscaled phase change devices.

The design of advanced functionality in superconducting electronics usually focuses on materials engineering, either in heterostructures or in compounds of unconventional quantum materials. Here we demonstrate a different strategy to bespoke function by controlling the 3D shape of superconductors on the micron-scale. As a demonstration, a large superconducting diode effect is engineered solely by 3D shape design of a conventional superconductor, ion-beam deposited tungsten. Its highly efficient diode behavior appears from its triangular cross-section when vortices break time-reversal and all mirror symmetries. Interestingly reciprocity is observed at four low-symmetry field angles where diode behavior would be expected. This can be understood as a geometric mechanism unique to triangular superconductors. Geometry and topology induce a rich internal structure due to the high-dimensional tuning parameter space of 3D microstructures, inaccessible to the conventional 2D design strategies in thin films.

The transparent hP4 phase of dense sodium (Na), stable above 200 GPa, has been computed to be an electride in which valence electrons are localised on interstitial lattice sites within the structure. However, there is no experimental evidence for this interstitial electron localisation in Na, or indeed in other high-density electride phases. Using static compression and single-crystal X-ray diffraction techniques, we have grown and studied a single-crystal sample of Na in the hP4 phase at 223 GPa. Using atomic form factors for hP4-Na derived from quantum crystallography techniques, we present experimental results to support the electride nature of this phase.

In structured adsorbents, achieving mesoporosity, crucial for efficient gas adosorption, is challenging, which restricts mass transport and accessibility to active sites. Here, we address this limitation by developing the first hierarchically porous honeycomb aerogels that replicate hexagonal pores at both the macro-level and micro-level wall structure. This design, inspired by nature's most efficient patterns, enables us to achieve CO₂ adsorption capacity (3.94 mmol g^-¹ at 298 K and 1 bar), selectivity (65.2 CO₂/N₂), and high specific surface area (370 m² g^-¹). The honeycomb aerogels are constructed from manganese dioxide (MnO₂) functionalized electrochemically exfoliated graphene (MEEG) and chitosan (CS). By optimizing the MnO₂ loading and the MEEG to CS weight ratio, we achieved dual-scale hexagonal porosity, enabling a hybrid physical and chemical adsorption mechanism. The hybrid adsorption leverages the rapid kinetics of chemisorption and ease of regeneration characteristic of physisorption, making these materials highly efficient. This highlights the synergy between enhanced surface accessibility of primary amine groups and selective adsorption properties, setting a new standard for hierarchically structured materials.

Topological magnon bands enable uni-directional edge transport without backscattering, enhancing the robustness of magnonic circuits and providing a novel platform for exploring quantum transport phenomena. Magnetic skyrmion lattices, in particular, host a manifold of topological magnon bands with multipole character and non-reciprocal dispersions. These modes have been explored already in the short and long wavelength limit, but previously employed techniques were unable to access intermediate wavelengths comparable to inter-skyrmion distances. Here, we report the detection of such magnons with wavevectors ∣q∣ ≃ 48 rad μm^-1 in the metastable skyrmion lattice phase of the bulk chiral magnet Cu₂OSeO₃ using Brillouin light scattering microscopy. Thanks to its high sensitivity and broad bandwidth various multipole excitation modes could be resolved over a wide magnetic field regime. Besides the known counterclockwise, breathing and clockwise modes with dipole character, quantitative comparison of frequencies and spectral weights to theoretical predictions enabled the additional identification of a quadrupole mode and, possibly, a sextupole mode. Our work highlights the potential of skyrmionic phases for the design of magnonic devices exploiting topological magnon states at GHz frequencies.

Charge density waves (CDW) appear as periodic lattice deformations which arise from electron-phonon and excitonic correlations and provide a path towards the study of condensate phases at high temperatures. While characterization of this correlated phase is well established via real or reciprocal space techniques, for systems where the mechanisms interplay, a macroscopic approach becomes necessary. Here, we demonstrate the application of polarization-resolved high-harmonic generation (HHG) spectroscopy to investigate the correlated CDW phase and transitions in TiSe₂. Unlike previous studies focusing on static crystallographic properties, the research examines the dynamic reordering that occurs within the CDW as the material is cooled from room temperature to 14 K. By linking ultrafast field-driven dynamics to the material's potential landscape, the study demonstrates HHG's unique sensitivity to highly correlated phases and their strength. The findings reveal an anisotropic component below the CDW transition temperature, providing insights into the nature of this phase. The investigation highlights the interplay between linear and nonlinear optical responses and their departure from simple perturbative dynamics, offering a fresh perspective on correlated quantum phases in condensed matter systems.

The year 2011 marked a breakthrough in material science innovation with the discovery of MXenes, an emerging family of two-dimensional transition metal-based nanomaterials. Owing to their distinctive properties, MXenes have rapidly surfaced as transformative materials, particularly in energy-storage and nanomedicine. In this review, we systematically explore the evolution of MXene synthesis, from its discovery to current advancements, focussing on their bioengineering applications, through a meta-analytic and bibliometric lens. We discuss synthesis methods, ranging from hydrofluoric acid (HF)-based etching to non-HF approaches, along with post-synthesis processes like intercalation, delamination and surface functionalization, that tailor MXene properties for biomedical therapeutics. We also overview key microscopy, spectroscopy and diffraction-based characterization methods, to understand their structure and functionality. Additionally, discussion on artificial intelligence (AI)-driven innovations highlights the significant shift in material science. By connecting synthesis methods with resulting characteristics and meta-analyses trends, this review emphasizes MXenes' transformative potential in regenerative therapeutics and diagnostics.