Compiled by: Wei Jiu
Nature, 23 May 2024, Vol 629, Issue 8013
Astronomy
The solar dynamo begins near the surface
▲ Authors: Geoffrey M. Vasil, Daniel Lecoanet, Kyle Augustson, Keaton J. Burns, Jeffrey S. Oishi, Benjamin P. Brown, et al.
▲ Link:
https://www.nature.com/articles/s41586-024-07315-1
▲ Abstract:
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating region of sunspot emergence appears around 30° latitude and vanishes near the equator every 11 years. Moreover, longitudinal flows called torsional oscillations closely shadow sunspot migration, undoubtedly sharing a common cause.
Contrary to theories suggesting deep origins of these phenomena, helioseismology pinpoints low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface shear layer. Within this zone, inwardly increasing differential rotation coupled with a poloidal magnetic field strongly implicates the magneto-rotational instability, prominent in accretion-disk theory and observed in laboratory experiments. Together, these two facts prompt the general question: whether the solar dynamo is possibly a near-surface instability.
Here we report strong affirmative evidence in stark contrast to traditional models focusing on the deeper tachocline. Simple analytic estimates show that the near-surface magneto-rotational instability better explains the spatiotemporal scales of the torsional oscillations and inferred subsurface magnetic field amplitudes. State-of-the-art numerical simulations corroborate these estimates and reproduce hemispherical magnetic current helicity laws. The dynamo resulting from a well-understood near-surface phenomenon improves prospects for accurate predictions of full magnetic cycles and space weather, affecting the electromagnetic infrastructure of Earth. Physics
Lithium tantalate photonic integrated circuits for volume manufacturing
▲ Authors: Chengli Wang, Zihan Li, Johann Riemensberger, Grigory Lihachev, Mikhail Churaev, Wil Kao, et al.
▲ Link:
https://www.nature.com/articles/s41586-024-07369-1
▲ Abstract:
Electro-optical photonic integrated circuits (PICs) based on lithium niobate (LiNbO3) have shown significant potential due to the high Pockels coefficient of the material. This has enabled the development of linear and high-speed modulators operating at complementary metal–oxide–semiconductor voltage levels for applications such as data center communications, high-performance computing, and AI photon accelerators.
However, the industrial application of this technology is hindered by the high cost per wafer and limited wafer size. The high cost is a result of the lack of high-volume applications in other fields that have accelerated the adoption of silicon-on-insulator (SOI) photonics driven by substantial investments in microelectronics.
In this study, a low-loss PIC made of lithium tantalate (LiTaO3) is presented. LiTaO3, already used commercially for 5G radiofrequency filters, allows for scalable and cost-effective manufacturing. LiTaO3 exhibits similar or even superior performance to LiNbO3 in certain cases. Results show that using a deep ultraviolet (DUV) stepper-based manufacturing process, LiTaO3 can be etched to create low-loss (5.6 dB m-1) PICs.
The study demonstrates a LiTaO3 Mach–Zehnder modulator (MZM) with a half-wave voltage–length product of 1.9 V cm and an electro-optic bandwidth of up to 40 GHz. Compared to LiNbO3, LiTaO3 has significantly lower birefringence, enabling high-density circuits and broadband operation across all telecommunication bands. Additionally, the platform supports the generation of soliton microcombs. This work lays the groundwork for the scalable manufacture of low-cost and high-volume next-generation electro-optical PICs. Materials Science
Selenium-alloyed tellurium oxide for amorphous p-channel transistors
▲ Authors: Ao Liu, Yong-Sung Kim, Min Gyu Kim, Youjin Reo, Taoyu Zou, Taesu Choi, et al.
▲ Link:
https://www.nature.com/articles/s41586-024-07360-w
▲ Abstract:
Compared to polycrystalline semiconductors, amorphous semiconductors offer inherent cost-effective, simple, and uniform manufacturing. Traditional amorphous hydrogenated silicon falls short in electrical properties, necessitating the exploration of new materials.
The emergence of high-mobility amorphous n-type metal oxides (such as a-InGaZnO) and their integration into thin-film transistors (TFTs) have driven advancements in modern large-area electronics and new-generation displays. However, finding a comparable p-type counterpart has been challenging, hindering the progress of complementary metal-oxide-semiconductor technology and integrated circuits.
This study introduces a groundbreaking design strategy for amorphous p-type semiconductors by incorporating high-mobility tellurium into an amorphous tellurium suboxide matrix. It demonstrates its application in high-performance, stable p-channel TFTs, and complementary circuits. Theoretical analysis reveals a delocalized valence band from tellurium 5p bands with shallow acceptor states, enabling excess hole doping and transport.
Selenium alloying suppresses hole concentrations, promotes p-orbital connectivity, and achieves high-performance p-channel TFTs with an average field-effect hole mobility of around 15 cm2 V-1 s-1 and on/off current ratios of 106~107. These devices exhibit wafer-scale uniformity and long-term stability under bias stress and ambient aging. This research represents a critical step towards establishing commercially viable amorphous p-channel TFT technology and complementary electronic devices in a cost-effective and industry-compatible manner. Electronic Engineering
Full-color 3D holographic augmented reality displays with metasurface waveguides
▲ Authors: Manu Gopakumar, Gun-Yeal Lee, Suyeon Choi, Brian Chao, Yifan Peng, Jonghyun Kim, et al.
▲ Link:
https://www.nature.com/articles/s41586-024-07386-0
▲ Abstract:
Emerging spatial computing systems seamlessly overlay digital information onto the physical environment observed by users, enabling revolutionary experiences in entertainment, education, communication, and training. However, the widespread adoption of augmented reality (AR) displays has been hindered by the bulky volume of their light engine projection optics and their inability to accurately represent three-dimensional (3D) depth cues for virtual content.
The research team introduces a holographic AR system that addresses these challenges through a unique combination of inverse-designed full-color metasurface gratings, a compact dispersion-compensating waveguide geometry, and AI-driven holography algorithms. These components are co-designed to eliminate the need for large collimation optics between the spatial light modulator and the waveguide, presenting vivid full-color 3D AR content in a compact device.
To provide unprecedented visual quality with this prototype, the research team developed an innovative image formation model that merges a physically precise waveguide model with learning components automatically calibrated using camera feedback. This distinctive co-design of a nanophotonic metasurface waveguide and AI-driven holographic algorithms represents a significant advancement in creating visually captivating 3D AR experiences in a compact wearable device. Chemistry
Observation of a promethium complex in solution
▲ Authors: Darren M. Driscoll, Frankie D. White, Subhamay Pramanik, Jeffrey D. Einkauf, Bruce Ravel, Dmytro Bykov, et al.
▲ Link:
https://www.nature.com/articles/s41586-024-07267-6
▲ Abstract:
Lanthanide rare-earth metals are widely used in modern technology, but the chemistry of the 61st element, promethium (Pm), remains poorly understood. Pm is highly radioactive and challenging to access as a lanthanide element. Despite its significance, experimental studies on Pm within the lanthanide series have been scarce, hindering a comprehensive understanding of the lanthanide contraction phenomenon, a fundamental aspect referenced in chemistry textbooks.
The research team has demonstrated the stable chelation of the 147Pm radioactive isotope (with a half-life of 2.62 years) in aqueous solution using a newly synthesized organic diglycolamide ligand. Through synchrotron X-ray absorption spectroscopy and quantum chemical calculations, they investigated the resulting homoleptic PmIII complex, determining the coordination structure and bond distance of promethium. These key insights enable a thorough structural analysis of a complete set of isostructural lanthanide complexes, capturing the lanthanide contraction in solution based solely on experimental observations. The study reveals an accelerated bond shortening at the beginning of the lanthanide series, linked to the separation trends exhibited by diglycolamides. Characterizing the radioactive PmIII complex in a water environment enhances our understanding of intra-lanthanide behavior, as well as the chemistry and separation of f-block elements. Boron catalysis in a designer enzyme
▲ Authors: Lars Longwitz, Reuben B. Leveson-Gower, Henriëtte J. Rozeboom, Andy-Mark W. H. Thunnissen & Gerard Roelfes
▲ Link:
https://www.nature.com/articles/s41586-024-07391-3
▲ Abstract:
Enzymes are playing an increasingly crucial role in enhancing the eco-friendliness and effectiveness of chemical production. However, due to the relatively limited range of reaction mechanisms of enzymes, their versatility in applications significantly lags behind chemical catalysts. The creation of enzymes with non-biological functionalities has opened up new reaction pathways beyond nature's traditional scope, paving the way for fully customizable biocatalysis.
In this study, a genetically encoded boronic acid-containing designer enzyme is introduced, exhibiting organocatalytic activity that surpasses what natural or engineered biocatalysts can achieve. This boron enzyme facilitates the kinetic resolution of hydroxyketones through oxime formation, with essential interactions with the protein scaffold aiding in catalysis. Through directed evolution, a variant with natural enzyme-like enantioselectivities for various substrates was developed.
The unique activation mechanism of the boron enzyme was confirmed using X-ray crystallography, high-resolution mass spectrometry (HRMS), and 11B NMR spectroscopy. The research highlights that genetic code expansion can lead to the creation of evolvable enantioselective enzymes that rely on external catalytic components like boronic acids, enabling access to reaction mechanisms beyond the catalytic promiscuity of natural or engineered enzymes.
