Comment

Electrons in solids carry orbital angular momentum in diverse non-equilibrium situations. This orbital current is often overlooked when considering electronic transport. Here we discuss how recent studies of orbital current are enabling more opportunities for technological advancements rooted in angular momentum.

An essential part of developing organic mixed ionic–electronic conducting materials and organic electrochemical transistors is consistent and standardized reporting of the product of charge carrier mobility and volumetric capacitance, the μC* product. This Comment argues that unexpected changes in transistor channel resistance can overestimate this figure of merit, leading to a confusion of comparisons in the literature.

In many concentrated alloys of current interest, the observation of diffuse superlattice intensities by transmission electron microscopy has been attributed to chemical short-range order. We briefly review these findings and comment on the plausibility of widespread interpretations, noting the absence of expected peaks, conflicts with theoretical predictions, and the possibility of alternative explanations.

The study of point defects in non-metallic crystals has become relevant for an increasing number of materials applications. Progress requires a foundation of consistent definitions and terminology. This Comment clarifies the underlying definitions of point defects, encourages the correct use of relative charge for their description and emphasizes their recognition as quasiparticles.

The steel industry in China has an important role in reducing national and global carbon emissions, demanding integrated actions and efforts across policies, industry and science to achieve the goal of carbon neutrality.

The success of silicon photonics is a product of two decades of innovations. This photonic platform is enabling novel research fields and novel applications ranging from remote sensing to ultrahigh-bandwidth communications. The future of silicon photonics depends on our ability to ensure scalability in bandwidth, size and power.

Organic semiconductors based on molecular or polymeric π-conjugated systems are now used at scale in organic light-emitting diode (OLED) displays and show real promise in thin-film photovoltaics and transistor structures. Here, we address recent progress in understanding and performance for OLEDs and for organic photovoltaics.

Metal–organic frameworks, porous coordination network materials constructed with metal ions and organic molecules, have grown over the past 20 years into an innovative chemistry that has contributed to solutions for the problems faced by humanity in the environment, resources, energy and health.

Soft matter has evolved considerably since it became recognized as a unified field. This has been driven by new experimental, numerical and theoretical methods to probe soft matter, and by new ways of formulating soft materials. These advances have driven a revolution in knowledge and expansion into biological and active matter.

Materials and surface sciences have been the driving force in the development of modern-day lithium-ion batteries. This Comment explores this journey while contemplating future challenges, such as interface engineering, sustainability and the importance of obtaining high-quality extensive datasets for enhancing data-driven research.

Semi-synthetic goldilocks material design integrates the tunable characteristics of synthetic materials and the refined complexity of natural components, enabling for the progress of biomaterials across length scales. Accelerated translational success may thus be possible for more personalized and accessible products.

Structural materials are critical components for our daily lives and industries. This Comment highlights the emerging concepts in structural materials over the past two decades, particularly the multi-principal element alloys, heterostructured materials and additive manufacturing that enables the fabrication of complex architectures.

Quantum materials show emergent electronic properties and related functions that are profoundly described by quantum mechanics beyond the semi-classical picture of electrons. Here, key developments and progress in the last two decades are surveyed and future challenges outlined.

Twentieth-century utopian visions of a space-age future have been eclipsed by dystopian fears of climate change and environmental degradation. Avoiding such grim forecasts depends on materials innovation and our ability to predict and plan not only their behaviour but also their sustainable manufacture, use and recyclability.

Synthetic stimuli-responsive systems have become increasingly sophisticated and elegant at the nanoscale. This Comment discusses how rationally designed molecular systems capable of dynamic motions can be deployed in macroscopically porous metal–organic frameworks and respond to various stimuli.

Automated experiments can accelerate research and development. ‘Flexible automation’ enables the cost- and time-effective design, construction and reconfiguration of automated experiments. Flexible automation is empowering researchers to deploy new science and technology faster than ever before.

New classes of functional soft materials show promise to revolutionize robotics. Now materials scientists must focus on realizing the predicted performance of these materials and developing effective and robust interfaces to integrate them into highly functional robotic systems that have a positive impact on human life.

Strong light–matter coupling in quantum cavities provides a pathway to break fundamental materials symmetries, like time-reversal symmetry in chiral cavities. This Comment discusses the potential to realize non-equilibrium states of matter that have so far been only accessible in ultrafast and ultrastrong laser-driven materials.

Electron microscopy touches on nearly every aspect of modern life, underpinning materials development for quantum computing, energy and medicine. We discuss the open, highly integrated and data-driven microscopy architecture needed to realize transformative discoveries in the coming decade.

Classical experiments from solid-state electrochemistry can be used to determine the charge of ions in solids. This Comment also clarifies how the charge of point defects fits with the standard picture of ionic charge, and highlights differences between these electrochemical experiments and methods that probe electrons directly.