A virus is made up of a protein shell, the $capsid$, protecting its genetic material, and that’s all. The subunits of the shell are arranged in a two-dimensional structure, held in place by a fine interplay between short-range and electrostatic interactions. The authors show that thermal dissociation of the capsid proceeds through a two-dimensional phase transition, providing direct quantitative insight into the strengths of the interactions and their variations in different ionic environments.

Deterministic control and detection of its charge state with high spatial resolution are what make the nitrogen-vacancy (N-$V$) center in diamond appealing for nanoscale quantum sensing and biological tracking. Usually high laser power is needed, though, which induces photodamage and decreases sensitivity. By also applying a weak $near-infrared$ laser, the authors significantly accelerate charge-state conversion by $visible$ photons, permitting decreased laser power for the subsequent nanoscopy. This could help to realize high spatial resolution and sensitivity, particularly for work on live cells.

Lead halide perovskite solar cells have already reached 22% efficiency, but the physical reasons $why$, and the limiting processes, remain unclear. The authors show that $photon$ $recycling$ (emission and reabsorption) causes unusually large carrier diffusion lengths in this class of photovoltaic absorber, with direct evidence of strong band-to-band transitions and efficient radiative recombination. These results will drive the improvement of such solar cells.

Despite its use since antiquity, steel still retains some mystery. For example, the origin of its key pearlite phase has remained elusive, despite intense research in recent decades. The present study describes an autocatalytic path to pearlite formation, in which the magnetism of iron plays a crucial role. This experimentally realistic mechanism of the first-order phase transition differs from both classical nucleation and spinodal decomposition, and may also be relevant to the decay of metastable states in other systems.

Despite over a decade of study, spin relaxation in the two-dimensional electron gas (2DEG) of silicon quantum wells and surfaces is not well understood. The authors show that, contrary to popular belief, electron spin relaxation in the Si 2DEG could be significantly affected by impurity scattering. This work provides a fresh understanding of the physics of spin-based information processing, and should be useful in guiding the development of silicon-based spintronics and quantum computation.

As spin-transfer-torque magnetic random-access memory finally enters mass production, there is great interest in enhancing performance using write schemes based on spin-orbit torque (SOT), which afford speed, reliability, and CMOS compatibility. A major issue, though, is finding materials for heterostructures that yield large SOT, perpendicular magnetic anisotropy, and low resistivity. So far, only platinum fulfills all of these requirements. The authors find that, despite its relatively low atomic number, palladium also allows efficient spin-orbit torques when interfaced with a ferromagnet.

A virus is made up of a protein shell, the $capsid$, protecting its genetic material, and that’s all. The subunits of the shell are arranged in a two-dimensional structure, held in place by a fine interplay between short-range and electrostatic interactions. The authors show that thermal dissociation of the capsid proceeds through a two-dimensional phase transition, providing direct quantitative insight into the strengths of the interactions and their variations in different ionic environments.

Ultrafast acoustics in nitride-based semiconductor nanostructures have been investigated in the wurtzite phase, but, due to piezoelectricity and internal strain, such structures are not good for photonic applications. Here optical interferometry is used to demonstrate that $zinc$ $blende$ nitride quantum wells, which are not affected by piezoelectricity, can serve as photonic-phononic devices, such as strain detectors. The authors exploit the quantum wells’ narrow spectral range of high photoelastic efficiency, centered in the near ultraviolet, to achieve high spatial and temporal resolution.

In a spectroscopic gamma-ray scintillation detector, hot and thermalized transport, trapping, and recombination in multiple kinetic orders set the performance characteristics on which security, physics, and medical applications depend. CsI:Tl is the classic scintillator, yet even in it the details of these processes are still not fully understood. In this study, computational modeling reveals the origins of both recent and old observations about the spatial and temporal characteristics of the carrier interactions. This insight allows for improved material engineering of spectroscopic radiation detectors.

Deterministic control and detection of its charge state with high spatial resolution are what make the nitrogen-vacancy (N-$V$) center in diamond appealing for nanoscale quantum sensing and biological tracking. Usually high laser power is needed, though, which induces photodamage and decreases sensitivity. By also applying a weak $near-infrared$ laser, the authors significantly accelerate charge-state conversion by $visible$ photons, permitting decreased laser power for the subsequent nanoscopy. This could help to realize high spatial resolution and sensitivity, particularly for work on live cells.

Organic electrochemical transistors (OECTs) are increasingly studied for sensing applications. While analyzing and maximizing OECT signal has been emphasized, noise has been mostly ignored, even though it limits a sensor’s resolution. The authors demonstrate that $1/f$ noise in OECTs is due to charge fluctuations near or within the channel material. The magnitude of this noise is similar to that observed in graphene transistors, and only slightly higher than in devices based on carbon nanotubes or silicon nanowires. For best results, design large-area channels.

Combining classical communication with quantum security, while maintaining practical bit rates, has been a goal for many years. The author proposes merging a classical signal with a proven, secure system for quantum key distribution (QKD). The QKD system is based on attenuated reflection of the classical signal, allowing it to securely communicate information while simultaneously building the shared random bits that provide provable security. This system has several advantages over other approaches, including not requiring on-demand single-photon or entangled-state sources.

Making the strongest magnets from the cheapest, most readily available materials is of keen interest in producing electric motors for cars, for example. In this study, advanced simulations illustrate the potential for $a$ $priori$ optimization of nanocomposite materials for permanent magnets. In particular, these simulations reveal that—in contrast to common belief—either perfect exchange coupling between magnetically soft and hard phases, or an elongated shape for hard grains, can seriously $reduce$ the performance of the resulting magnets.

Quantum information processing based on light has invigorated research on the production and detection of single photons. The authors present an innovative detection scheme for weak microwave signals, based on a superconducting current-biased Josephson junction. In contrast to detectors that absorb photons, this system is optimized such that the amplitude of the classical photon field triggers detection.

The manipulation of spin waves is the basis of $magnonics$, one approach to the next generation of hardware for logic and data storage. The authors demonstrate the voltage-controlled transfer of spin-wave energy between adjacent ferrimagnetic-ferroelectric heterostructures. The coupling efficiency of the laterally coupled multiferroics can be tuned by independently varying applied magnetic and electric fields, which offers enticing prospects for magnonic devices.

The chirality (handedness) of molecules is important in physics, chemistry, and especially biology, where enantiomers can have drastically different effects on a living system. Chiral rodlike molecules can self-assemble into a liquid-crystalline helical structure with orientational order. The authors show that such a structure differentiates chiral guest molecules diffusing through it: Guests of the same handedness traverse the host more rapidly than those of opposite orientation. This could be used to separate enantiomers, yielding pure pharmaceuticals, for example.

Optical switching and generating and shaping short laser pulses rely on nonlinear absorbing elements, whose operation is usually determined by material properties. The authors present a $structured$ saturable absorber based on quantum-inspired design of waveguide arrays, superior in performance to designs based on directional couplers or uniform waveguide arrays. In particular, their absorber provides tunability and a very sharp on/off transition in transmission, which are promising for next-generation mode-locked lasers and photonic logic circuits.

Intermediate-band semiconductors have attracted much interest in the photovoltaic community, as they are expected to allow higher solar-cell efficiencies than traditional absorbers. The authors directly measure minority-carrier lifetimes in Ga(P,As,N), only to find that these times are too short for efficient solar cells. The observed lifetimes seem not to be fundamental material properties, though, but rather the result of recombination at defects. This identifies material quality as possibly the most important issue preventing the development of efficient solar cells based on these semiconductors.

Treating a solid surface to make it superhydrophobic (like a lotus leaf, for example) yields high droplet mobility upon it, with a reduced droplet footprint. However, a large footprint is required for efficient transfer of energy and momentum from a surface acoustic wave (SAW) to the droplet. To solve this dilemma, the authors propose a slippery liquid-infused porous surface (SLIPS) to remove contact-line pinning and provide high droplet mobility, while retaining a $large$ droplet footprint. This significantly reduces the threshold power for moving droplets with SAWs in acoustofluidic applications.

The authors use a single laser beam with synchronously modulated polarization and phase to trap atoms in a superposition state, decoupled from the light. Thanks to the linear architecture of this setup, it can serve as a compact, high-performance vapor-cell atomic clock. Such systems based on coherent population trapping are desired as successors to the well-known rubidium clock, particularly for applications in navigation and telecommunication. This setup offers frequencies an order of magnitude more stable than from a typical industrial clock.

It would be very useful if a solar cell’s power conversion efficiency could be measured without using electrical contacts, but is that really possible? The authors show that it is, by using time-resolved photoluminescence to characterize a working GaAs photovoltaic cell. This technique enables the identification of the charge-separation time constants that control current generation at the point of maximum power—key insight for engineering better solar panels.

Ferroelectric diodes are promising for fast, low-power nonvolatile memory, but a major roadblock to this technology is a lack of reliability and reproducibility, the origins of which remain poorly understood. Through experiment and modeling, the authors show that the electroresistance ratio, resistive-switching polarity, and high- and low-resistance states all can be significantly affected by interfacial charge injection and trapping in such a device. This work carries important implications for the development of reliable resistive-switching memory.

Surface plasmons (SPs) are key excitations for manipulating light in two dimensions, as in integrated optical circuits on chips. Here the authors show how to filter, in selected directions, the signal due to SP motion in a collimating device. Considering both the classical and quantum optical regimes, they interpret their findings in terms of a propagative electromagnetic local density of states. This approach could also be used in other quantum-technology contexts, $e.g.$ to optimize the coupling efficiency of quantum emitters.

As spintronics continues to replace conventional electronics, devices that produce oscillatory signals are needed in particular. They are usually based on spin-transfer torque, but this study offers an alternative, based on feedback of spin current into a magnetic tunnel junction (MTJ). A combination of thermal fluctuations, magnetoresistance, and the spin Hall effect can induce periodic precessional states in the MTJ’s free layer, significantly reducing the critical current for oscillations and improving their quality factor.

Beams of “squeezed” light have important applications in quantum metrology and gravitational-wave detection. The authors generate twin beams of correlated photons using parametrically amplified four- and six-wave mixing in a nonlinear optical crystal. This medium offers several advantages, such as better on-chip integration than atomic vapors, plus a longer coherence time than traditional optical materials. These achievements can also find potential application in all-optical communication and quantum storage of light in photonic circuits.