From any standpoint—historical, practical, or theoretical—glass physics is a field crying out for better appreciation, new applications, and stronger treatment.

Radio-frequency metamaterials with negative magnetic response hold great promise for both reducing the size and improving the performance of antennas for wireless applications. Using temperature to modify the superfluid density in a three-dimensional superconducting metamaterial, the authors demonstrate continuous in situ tunability of the effective permeability, from negative to positive values, without resorting to lossy lumped elements.

Helium is a precious resource, and cryogenic facilities worldwide operate under the threat of supply problems. Using thermodynamic principles, the authors reveal a method for more efficient small-scale helium liquefaction. This technology improves rates and lowers energy consumption by employing higher pressure during the liquefaction process. Thus the next generation of cryocooler-based liquefiers will enable convenient production of liquid helium locally within small laboratories, medical centers, and hospitals everywhere.

Microscopic propellers that transport and release cargo in fluid media are of growing interest for applications in biomedicine, targeted drug delivery, and microfluidics. The authors demonstrate a general method for assembling and propelling maneuverable colloidal carpets, which can be steered in any direction of the plane by modulating a magnetic field. They also reveal a hydrodynamic “conveyor-belt effect” generated by the moving structure that may be useful in fluid-dynamics applications.

To produce the microfluidic equivalent of the ubiquitous multiwell plate for lab-on-a-chip assays, the authors show how thousands of nanoliter droplets can be precisely dispensed from an ordered array of microfabricated anchors. Their study of the underlying physics shows that after fluid has spontaneously attached to the anchors, it then sheds droplets through the emergence of a finite-time singularity. This discovery enables the production of large numbers of well regulated droplets in a simple microfluidic device.

Helium is a precious resource, and cryogenic facilities worldwide operate under the threat of supply problems. Using thermodynamic principles, the authors reveal a method for more efficient small-scale helium liquefaction. This technology improves rates and lowers energy consumption by employing higher pressure during the liquefaction process. Thus the next generation of cryocooler-based liquefiers will enable convenient production of liquid helium locally within small laboratories, medical centers, and hospitals everywhere.

Ultrafast dynamics in molecules, nanostructures, and interfaces are commonly studied using pump-probe spectroscopy. The bandwidth for this approach has been limited to about 1000 cm${}^{-1}$ in the midinfrared region. The authors develop an upconversion technique for femtosecond-scale detection, and demonstrate an ultrabroadband pump-probe system with a spectral range of 200—5000 cm${}^{-1}$. Their system dramatically improves access to the energy regions of interest for investigating the relaxation of optically excited systems as diverse as proteins, liquid water, semiconductors, and topological insulators.

Microscopic propellers that transport and release cargo in fluid media are of growing interest for applications in biomedicine, targeted drug delivery, and microfluidics. The authors demonstrate a general method for assembling and propelling maneuverable colloidal carpets, which can be steered in any direction of the plane by modulating a magnetic field. They also reveal a hydrodynamic “conveyor-belt effect” generated by the moving structure that may be useful in fluid-dynamics applications.

The discovery of light emission from metal-insulator-metal tunnel junctions in the 1970s suggested a low-energy, broadband source of visible light. Presently this technology is also of interest for generating subwavelength surface plasmons electrically. The authors show that inelastic electron tunneling excitation is potentially 10${}^5$ times as efficient for producing mid-infrared plasmons in graphene than in metal, offering great promise for on-chip integrated nanophotonics.

Presently much research is devoted to recapturing waste heat for improved energy efficiency. Here the authors study an array of parallel “dirty” semiconductor nanowires, configured as a field-effect transistor. For temperatures at which electrons move in phonon-assisted hops, large figures of merit and output powers are obtained if the impurity bands of the nanowires are depleted by applying a gate voltage. Synergy between phonon activation and gate-tunable particle-hole asymmetry predicts a versatile thermoelectric converter, enabling nanoscale heat management on a chip.

A thermoelectric generator can convert waste heat (such as from a car engine or municipal power plant) into useful electrical energy. In this study a device based on gate-modulated semiconductor nanowires is projected to have high efficiency and power output, its gate voltage being optimized on the fly for varying temperature differences and external loads. The approach takes advantage of the interplay between microscopic parameters of the wires and thermodynamic parameters of the leads in the nonlinear regime. Based on these results the system is projected to be robust, scalable, and industrially promising.

Quantum random-number generators (QRNGs) play a decisive role in protocols for encrypted communication. Unfortunately, classical noise often spoils both the integrity and speed of such quantum devices. The authors demonstrate a new framework to harness maximum randomness without compromising security, and which allows for more cost-effective and smaller units. This work paves the way toward a reliable, high-bit-rate, and environmentally immune QRNG for information-security applications.

Scintillators luminesce when exposed to ionizing radiation, and thus find application from detectors in high-energy and medical physics to the humble fluorescent light bulb. The authors study a class of materials with electronic structure featuring discrete bands (reminiscent of those in intermediate-band solar cells) that promote efficient emission from bound excitons. This discovery should overcome barriers to efficient energy transfer and inform future exploration as well.

To produce the microfluidic equivalent of the ubiquitous multiwell plate for lab-on-a-chip assays, the authors show how thousands of nanoliter droplets can be precisely dispensed from an ordered array of microfabricated anchors. Their study of the underlying physics shows that after fluid has spontaneously attached to the anchors, it then sheds droplets through the emergence of a finite-time singularity. This discovery enables the production of large numbers of well regulated droplets in a simple microfluidic device.

Intermediate-band solar cells (IBSCs) offer efficiency exceeding the Shockley-Queisser limit of about 34% for basic, single-junction cells. The authors demonstrate the two-photon absorption processes believed to be the basis for boosted efficiency in IBSCs, including the temperature-dependent increase in quantum efficiency due to absorption of infrared light. They also explain the importance of using a blocking layer in a working device. Such discoveries carry us further into a future based on clean, renewable energy.

The authors experimentally identify the stabilizing effect of wettability in a porous matrix during the immiscible displacement of a viscous fluid (such as oil) by a much less viscous one (such as water). By altering the wettability of the medium from drainage (contact angle $\theta$ = 5°) to imbibition ($\theta$ = 120°), the classical viscous-fingering instability is stabilized and even completely suppressed at low capillary numbers (i.e. low injection rates), making the invading fluid better at pushing out the defending fluid. These results have implications for improving oil recovery, CO${}_2$ sequestration, and fuel-cell design.

Cavity quantum optomechanical systems are promising in several domains of applications, from mechanical sensing to quantum information processing. However, to unleash the full potential of this technology, significant improvements in reliability and integrability of optomechanical devices are needed. The authors propose a silicon resonator, built using MEMS technology, with a design affording both low optical and mechanical losses. This device is tailored to operate at cryogenic temperatures, with intracavity power of hundreds of watts.

Radio-frequency metamaterials with negative magnetic response hold great promise for both reducing the size and improving the performance of antennas for wireless applications. Using temperature to modify the superfluid density in a three-dimensional superconducting metamaterial, the authors demonstrate continuous in situ tunability of the effective permeability, from negative to positive values, without resorting to lossy lumped elements.

For everyday applications, low-voltage devices are desirable, but in a typical organic light-emitting diode (OLED) the turn-on voltage is rather high, greater than the HOMO-LUMO energy gap of the emitter. In this study a combination of materials is strategically selected to construct an OLED in which the energy of emitted photons is higher than that supplied by the applied electrical potential. The mechanism is based on an Auger process at the organic heterojunction, where the relevant energy gap is between the LUMO of the acceptor and the HOMO of the donor.