Browse Articles

Observation of transient trion induced by ultrafast charge transfer in graphene/MoS2 heterostructure

Van der Waals (vdW) heterostructures constructed from transition metal dichalcogenidess provide an ideal platform for exploring various quasiparticle behaviors, with trion—composed of neutral exciton and charged carrier—being a notable example. There are typically three methods to generate trion: electrical doping, chemical doping, and direct optical doping. The first two methods generate static trion, while the last gives rise to transient trion. Here, we present an indirect optical doping approach to generate transient trion via ultrafast charge transfer (CT) and achieve control over the trion-to-exciton ratio by adjusting CT in Gr/MoS2 heterostructure. Furthermore, we demonstrated that dynamics of the transient trion generated with this method, which shows slightly longer lifetime than that of exciton accounted for the Coulomb interactions between trion and charged defect. This study provides fresh perspectives on the construction of desired quasiparticles, dynamical characterization, and the control of the many-body interaction in two-dimensional structure.

Chemical-state imaging of a mammalian cell through multi-elemental soft x-ray spectro-ptychography

Soft x-ray spectro-ptychography is a high-resolution chemical state imaging technique and has significant potential for the analysis of light-element-rich samples such as biological cells. We measured hyperspectral images of a whole mammalian neuronal cell at the nitrogen and oxygen absorption edges with soft x rays using the achromatic ptychography system CARROT developed at SPring-8 BL07LSU. We visualized and classified the intracellular structures based on the difference of chemical states, which are difficult to recognize in a monochromatic image. The method is expected to give insight into the relationship between intracellular structures and chemical states.

Single-frame statistical gating in a speckle pattern generated by the dynamic scattering in disordered medium

The propagation of coherent light in a dynamic disordered medium generates dynamic speckle patterns. The dynamics intrinsic to the disordered medium result in a shorter decorrelation time for the multiple scattering component (τcM) relative to the single scattering component (τcS). In this study, we propose a single-frame statistical gating strategy for the single and multiple scattering components in reflective wide-field imaging when the exposure time T satisfies the condition τcM<T<τcS. The spatial matrix representation is modeled as the sum of a negative exponential matrix, which represents the single scattering component, and a Gaussian matrix, which represents the multiple scattering component. The Marchenko–Pastur distribution and the Tracy–Widom distribution are employed in conjunction to calculate the moments of the single and multiple scattering components. The single-frame statistical gating method is validated using an electric field Monte Carlo simulation and demonstrated in vivo in brain imaging. Based on rotational invariance, a rotational sampling strategy is proposed to significantly improve the imaging quality of the single-frame statistical gating method. The single-frame statistical gating method greatly facilitates future applications in scenarios such as clinical and complex natural environments.

In dopant enabled resonant level for thermoelectric enhancements in PbSnGeTe3

Resonant level engineering is an effective strategy to increase the Seebeck coefficient of thermoelectric semiconductors for high performance. Herein, we report a significant enhancement of the thermoelectric performance of PbSnGeTe3 over a wide temperature region through the In doping induced resonant level. Due to the simultaneously strengthened effective mass by inducing resonant levels nearby the Fermi level and decreased carrier concentration, a considerably improved Seebeck coefficient is obtained in In-doped PbSnGeTe3 and thereby the greatly increased power factor. The decreased carrier concentrations resulting from In substitution can also suppress the electronic thermal conductivity for a decreased thermal conductivity. The enhanced power factor and reduced thermal conductivity finally contribute to an extraordinarily high average ZT of 0.93 between 300 and 773 K in PbSnGeTe3. These observations demonstrate the viability of resonant levels in advancing thermoelectric materials with intrinsically high carrier concentrations.

Revealing the twist-angle-dependent interlayer coupling in WS2/MoSe2 heterostructures

Periodic moiré superlattice structures in transition metal dichalcogenides (TMDs) heterostructures exhibit nanoscale tunable electronic and optical properties. Much effort has been devoted to understand the twist-angle-dependent optical properties of the TMDs heterostructures. Therefore, quickly determining the stacking angle of TMDs and constructing the desired moiré superlattice structure is crucial. Here, we investigate the twist-angle-dependent optical properties of WS2/MoSe2, finding that the out-of-plane Raman mode is a reliable marker for determining the stacking angle. The interlayer exciton energy, being close to that of MoSe2 excitons, is highly sensitive to material quality and fabrication, making it unsuitable for identifying the stacking angle. In contrast, the out-of-plane Raman peaks of WS2 and MoSe2 are more sensitive to changes in the stacking angle. The out-of-plane Raman mode of WS2 is enhanced more than fivefold in near 0° or 60° WS2/MoSe2 heterostructures, while the out-of-plane mode of MoSe2 is only significantly decreased in near 0° heterostructures. Combining the intensity of out-of-plane Raman mode of WS2 and MoSe2, near 0° and 60° heterostructures can be distinguished without the need for complex optical characterizations. These typical peaks offer researchers an efficient way to construct the desired moiré superlattice structures.

Metasurface-based single-pixel recognition through scattering media

Taking advantage of optoelectronic hybrid neural networks, we propose a metasurface-single-pixel hybrid neural network for object recognition. It employs only eight illumination patterns trained by the digital neural network to convolve the object from two-dimensional images into only eight intensity values measured by a single-pixel detector, achieving a 93.8% accuracy rate in handwritten digit recognition. Our work therefore paves an image-free way for metasurface-based object recognition using only a single-pixel detector, which exhibits its powerful information compression and accurate extraction capabilities coupled with a compact structural design.

Enhanced size-dependent efficiency of InGaN/AlGaN near-ultraviolet micro-LEDs

This study presents an approach for enhancing the external quantum efficiency (EQE) of multiple-quantum-well InGaN/AlGaN near-ultraviolet (NUV) micro-light-emitting diodes (micro-LEDs) without changing the epitaxial layer. Unlike the size-dependent EQE reduction observed in blue, green, and red micro-LEDs, the EQE of NUV micro-LEDs at high current densities (≥10 A/cm2) improves as the device dimensions shrink from 500 × 500 μm2 to 20 × 20 μm2. A 20 × 20 μm2 micro-LED achieves a peak EQE of 12.3%, compared to 8.60% for a larger 500 × 500 μm2 micro-LED. Experimental results attribute this EQE enhancement to improved light-extraction efficiency, driven by better current spreading. In larger micro-LEDs, pronounced current crowding causes carrier overflow from the active region, leading to reduced EQE at high current densities. These findings highlight the promising potential of NUV micro-LEDs for diverse applications.

Dead-zone-free single-beam atomic magnetometer based on free-induction-decay of Rb atoms

Free-induction-decay (FID) magnetometers have evolved as simple magnetic sensors for sensitive detection of unknown magnetic fields. However, these magnetometers suffer from a fundamental problem known as a “dead zone,” making them insensitive to certain magnetic field directions. Here, we demonstrate a simple experimental scheme for the dead-zone-free operation of a FID atomic magnetometer. Using a single laser beam containing equal strength of linear- and circular-polarization components and amplitude modulation at a low-duty cycle, we have synchronously pumped the rubidium (87Rb) atoms with both first- and second-order frequency harmonics. Such a pumping scheme has enabled us to observe the free Larmor precession of atomic spins at a frequency of ΩL (orientation) and/or 2ΩL (alignment) in a single FID signal, depending on the direction of the external magnetic field. We observed that the amplitude of the FID signal does not go to zero for any magnetic field direction, proving the absence of dead zones in the magnetometer. The magnetometer has a sensitivity in the range of 3.2–8.4 pT/Hz in all directions. Our experimental scheme can be crucial in developing miniaturized atomic magnetometers for various practical applications, including geomagnetic applications.

Residual-<i>ZZ</i>-coupling suppression and fast two-qubit gate for Kerr-cat qubits based on level-degeneracy engineering

Building large-scale quantum computers requires an interqubit-coupling scheme with a high on–off ratio to avoid unwanted crosstalk coming from residual coupling and to enable fast multi-qubit operations. We propose a ZZ-coupling scheme for two Kerr-cat qubits with a frequency-tunable coupler. By making four relevant states of the two Kerr-cat qubits quadruply degenerate, we can switch off the ZZ coupling. By partially lifting the level degeneracy, we can switch it on. We theoretically show that an experimentally feasible circuit model suppresses the residual ZZ coupling. Moreover, our circuit can realize RZZ(−π/2)-gate fidelity higher than 99.9% within 18 ns when decoherence is ignored. Our model includes the first-order terms in expansion beyond the rotating-wave approximation.

Lowering the coercive field of van der Waals ferroelectric NbOI2 with photoexcitation

Polarization switching in van der Waals ferroelectric materials driven by an electric field remains robust even at the atomic layer limit, paving the way for advances in the miniaturization and integration of ferroelectric devices. Thus, understanding the modulation of ferroelectric properties in two-dimensional ferroelectric materials is essential for their efficient nanoscale applications. NbOI2, a recently confirmed van der Waals ferroelectric, offers an ideal platform for investigating in-plane spontaneous polarization at the nanoscale. We explored the influence of laser excitation on the ferroelectric polarization properties of NbOI2. In multilayer NbOI2 devices with in-plane configurations, no significant current signals were detected along the c-axis or b-axis (the ferroelectric polarization axis) in the absence of illumination. However, under laser excitation, the material exhibited clear hysteresis loop behavior along both the c-axis and b-axis, indicating that laser excitation effectively reduces the coercive voltage. Furthermore, at the same excitation wavelength, the current peak along the c-axis was larger, with more pronounced hysteresis loops. Our experimental findings demonstrate that laser excitation can lower the coercive field in multilayer NbOI2 and induce different electrical hysteresis behavior along different crystallographic orientations, providing valuable insights for the development of NbOI2-based optoelectronic devices.

Toward model-free temperature diagnostics of warm dense matter from multiple scattering angles

Warm dense matter plays an important role in astrophysical objects and technological applications, but the rigorous diagnostics of corresponding experiments is notoriously difficult. In this work, we present a model-free analysis of x-ray Thomson scattering (XRTS) measurements on isochorically heated graphite obtained at the Linac Coherent Light Source at multiple scattering angles. We demonstrate that the recent imaginary-time thermometry technique works for scattering data that have been measured in both forward and backward scattering geometry. This opens up the way toward a rigorous quantification of nonequilibrium effects in future experiments, where XRTS measurements are being obtained from multiple scattering angles from the same sample.

Synthesizing spin–orbit couplings and symmetry-protected topological phase in acoustic metamaterials

Spin–orbit couplings (SOCs) underlie several key concepts of topological matter. However, acoustic waves lack intrinsic spin and SOCs, which makes some topological phases impossible. We develop in the present work a realistic scheme to synthesize simultaneously the intrinsic and Rashba–Dresselhaus SOCs in acoustic systems and explore the symmetry-protected topological phase induced by the SOCs. To be precise, we construct a two-leg ladder composed of acoustic resonators and linking tubes. Utilizing the concept of pseudospin, the spin-1/2 is encoded by the leg degree of freedom of the ladder, and meanwhile, the SOCs are achieved by engineering the couplings between resonators. We further highlight the emergence of the symmetry-protected topological phase respecting the chiral unitary (AIII) symmetry in such acoustic SOC lattices. This scheme is confirmed by the full-wave simulations. Our acoustic structure is within immediate experimental reach and enables the direct visualization of symmetry-protected topological boundary states, not yet been observed experimentally. Our results represent a route to synthesize the SOCs and will benefit an in-depth study of the spin–orbit physics in acoustics.

Quantum anomalous Hall effect for metrology

The quantum anomalous Hall effect (QAHE) in magnetic topological insulators offers great potential to revolutionize quantum electrical metrology by establishing primary resistance standards operating at zero external magnetic field and realizing a universal “quantum electrical metrology toolbox” that can perform quantum resistance, voltage, and current metrology in a single instrument. To realize such promise, significant progress is still required to address materials and metrological challenges—among which, one main challenge is to make the bulk of the topological insulator sufficiently insulating to improve the robustness of resistance quantization. In this Perspective, we present an overview of the QAHE; discuss the aspects of topological material growth and characterization; and present a path toward a QAHE resistance standard realized in magnetically doped (Bi,Sb)2Te3 systems. We also present guidelines and methodologies for QAHE resistance metrology, its main limitations and challenges, as well as modern strategies to overcome them.

Water-regulated viscosity-plasticity phase transitions in a peptide self-assembled muscle-like hydrogel

Statistical identification of cell type-specific spatially variable genes in spatial transcriptomics

Nonlinearity of the post-spinel transition and its expression in slabs and plumes worldwide

Abstract Phase transitions in the mantle control its internal dynamics and structure. The post-spinel transition marks the upper–lower mantle boundary, where ringwoodite dissociates into bridgmanite plus ferropericlase, and its Clapeyron slope regulates mantle flow across it. This interaction has previously been assumed to have no lateral spatial variations, based on the assumption of a linear post-spinel boundary in pressure and temperature. Here we present laser-heated diamond anvil cell experiments with synchrotron X-ray diffraction to better constrain this boundary, especially at higher temperatures. Combining our data with results from the literature, and using a global analysis based on machine learning, we find a pronounced nonlinearity in the post-spinel boundary, with its slope ranging from –4 MPa/K at 2100 K, to –2 MPa/K at 1950 K, and to 0 MPa/K at 1600 K. Changes in temperature over time and space can therefore cause the post-spinel transition to have variable effects on mantle convection and the movement of subducting slabs and upwelling plumes.

Tubulin tyrosination/detyrosination regulate the affinity and sorting of intraflagellar transport trains on axonemal microtubule doublets

Abstract Cilia assembly and function rely on the bidirectional transport of components between the cell body and ciliary tip via Intraflagellar Transport (IFT) trains. Anterograde and retrograde IFT trains travel along the B- and A-tubules of microtubule doublets, respectively, ensuring smooth traffic flow. However, the mechanism underlying this segregation remains unclear. Here, we test whether tubulin detyrosination (enriched on B-tubules) and tyrosination (enriched on A-tubules) have a role in IFT logistics. We report that knockout of tubulin detyrosinase VashL in Chlamydomonas reinhardtii causes frequent IFT train stoppages and impaired ciliary growth. By reconstituting IFT train motility on de-membranated axonemes and synthetic microtubules, we show that anterograde and retrograde trains preferentially associate with detyrosinated and tyrosinated microtubules, respectively. We propose that tubulin tyrosination/detyrosination is crucial for spatial segregation and collision-free IFT train motion, highlighting the significance of the tubulin code in ciliary transport.

Standard operating procedure combined with comprehensive quality control system for multiple LC-MS platforms urinary proteomics

Abstract Urinary proteomics is emerging as a potent tool for detecting sensitive and non-invasive biomarkers. At present, the comparability of urinary proteomics data across diverse liquid chromatography−mass spectrometry (LC-MS) platforms remains an area that requires investigation. In this study, we conduct a comprehensive evaluation of urinary proteome across multiple LC-MS platforms. To systematically analyze and assess the quality of large-scale urinary proteomics data, we develop a comprehensive quality control (QC) system named MSCohort, which extracted 81 metrics for individual experiment and the whole cohort quality evaluation. Additionally, we present a standard operating procedure (SOP) for high-throughput urinary proteome analysis based on MSCohort QC system. Our study involves 20 LC-MS platforms and reveals that, when combined with a comprehensive QC system and a unified SOP, the data generated by data-independent acquisition (DIA) workflow in urine QC samples exhibit high robustness, sensitivity, and reproducibility across multiple LC-MS platforms. Furthermore, we apply this SOP to hybrid benchmarking samples and clinical colorectal cancer (CRC) urinary proteome including 527 experiments. Across three different LC-MS platforms, the analyses report high quantitative reproducibility and consistent disease patterns. This work lays the groundwork for large-scale clinical urinary proteomics studies spanning multiple platforms, paving the way for precision medicine research.

Modulation of Co spin state at Co3O4 crystalline-amorphous interfaces for CO oxidation and N2O decomposition

A principle-based framework to determine countries’ fair warming contributions to the Paris Agreement

Abstract Equity is a cornerstone of global climate policy, yet differing perspectives mean that international agreement on how to allocate mitigation efforts remains elusive. A rich literature informs this question, but a gap remains in approaches that appropriately consider non-CO2 emissions and their warming contributions. In this study, we address this gap and define a global warming budget applicable to all anthropogenic greenhouse gases that is allocated to countries based on principles drawn from international treaties and environmental law. We find that by 2021 a range of 84 to 90 countries, including but not limited to all major developed countries, exhausted their budget share compatible with keeping warming to 1.5 °C (with 50% likelihood) under all allocation approaches considered in this study. A similar picture emerges for limiting warming to 2 °C (with 67% likelihood). A large group of countries will hence exceed their fair shares even if their pledges under the Paris Agreement represent their deepest possible emission reductions. Considerations of fairness should therefore start exploring aspects beyond domestic emissions reductions.