Dipolar particles are building blocks in several fields of science and technology, but making rings from interacting ferromagnetic colloids is challenging, due to strong thermal fluctuations at the microscale. This study shows that, under the right conditions, magnetic microparticles can $spontaneously$ form dipolar rings. The authors fabricate anisotropic hematite ellipsoids dispersed in water, which self-assemble into colloidal ribbons that transform into rings. These rings can be controlled with a static or oscillating magnetic field, to encircle, transport, and release a biological cell in a microfluidic device, for example.

The spins of point defects in silicon carbide are promising candidates for qubits and sensors under $ambient$ conditions. Unlike defect-bearing diamond, SiC is regarded as an industry-friendly platform, with an existing market for high-purity SiC wafers and a mature fabrication technology. The authors detect the magnitude and direction of a magnetic field using magnetic resonance with optical readout of the spin-3/2 states of silicon-vacancy defects in SiC, plus optimized pulse sequences for spin manipulation. This yields a solid-state quantum vector magnetometer in a material available for wafer-scale production.

Dipolar particles are building blocks in several fields of science and technology, but making rings from interacting ferromagnetic colloids is challenging, due to strong thermal fluctuations at the microscale. This study shows that, under the right conditions, magnetic microparticles can $spontaneously$ form dipolar rings. The authors fabricate anisotropic hematite ellipsoids dispersed in water, which self-assemble into colloidal ribbons that transform into rings. These rings can be controlled with a static or oscillating magnetic field, to encircle, transport, and release a biological cell in a microfluidic device, for example.

Even spintronic devices generate heat. Measuring the temperature in a nanoscale magnetic tunnel junction is important for developing next-generation technologies such as magnetic random-access memory (MRAM), as well as for distinguishing the underlying physical phenomena. The authors use interlayer exchange coupling to monitor a complex thermally assisted MRAM stack, probing Joule heating in real time. They separate the contribution of temperature from that of spin-transfer torque, and find that in some situations the magnetic moment rotates instead of switching.

A strong theme in applied physics research is the control of magnetism with electric (rather than magnetic) fields. Giant electroresistance can be used to this end in a ferroelectric tunnel junction (FTJ) by adding a material in which a metal-insulator transition is triggered by polarization switching in the ferroelectric. Half-doped manganites like La${}_{0.5}$(Sr,Ca)${}_{0.5}$MnO${}_3$ seem ideal for this, but epitaxial strain can profoundly modify their ground state. The authors use ${}^{55}$Mn NMR to study orbital and magnetic orderings in such epitaxial films, and they evaluate how the films evolve with strain and electronic bandwidth. Their results are key to engineering large tunneling electroresistance in FTJs.

In the growing field of quantum information science, nitrogen-vacancy ($NV$) defects in diamond are a leading candidate for hybrid systems that exploit the best features of coupled phonons, spins, and photons. Using the strong coupling of a nanoresonator’s vibrational modes to an embedded $NV$ center’s orbital degrees of freedom, the authors mechanically control the frequency and polarization of the optical transitions of the center. This could facilitate the development of photonic and phononic quantum networking, quantum computing hardware, and quantum control of mechanical oscillators using two-level systems.

Josephson parametric amplifiers (JPAs) are important tools in quantum information technology, and traveling-wave JPAs with extended bandwidth are especially desired for frequency multiplexing, $e.g.$ in qubit readout. So far these devices have required the four-wave mixing condition to operate. The author shows, however, that there is a way to realize $three-wave$ mixing, with negligible phase mismatch. This simple traveling-wave amplifier would offer large gain, wide bandwidth, and ultimately quantum-limited characteristics, outperforming its state-of-the-art four-wave counterparts.

The resistance of a thin film of nonmagnetic metal with strong spin-orbit coupling can be modulated by the magnetization of an adjacent ferromagnetic insulator. The authors use this phenomenon of $spin$ $Hall$ $magnetoresistance$ (SMR) to probe the surface of CoFe${}_2$O${}_4$, extracting information that cannot be obtained with any standard magnetometry technique. These results herald SMR as an important tool for mapping the complex surface magnetization of a ferromagnetic insulator, $e.g.$ to design a spintronic device.

Do you want the job done right, or do you want it done fast? No matter the platform, processors based on circuit quantum electrodynamics can require a significant wait after measurement, to allow leftover photons to exit the readout resonators. The authors demonstrate two methods that minimize dead time, even when a resonator is driven $nonlinearly$. This reduces the buildup of errors in an error-correction cycle, so we can enjoy speed $and$ accuracy in quantum computing.

As we follow Moore’s Law and pack more and more components onto each computer chip, we must extend the limits of manufacturing. Looking ahead, efficient sources of light at a wavelength around 6.7 nm are needed for beyond-extreme-ultraviolet (BEUV) lithography, to create integrated circuits beyond the 7-nm logic node. This study measures and models plasmas of Gd and Tb, prepared using a single laser tuned over a broad range of parameters. These plasmas do emit at the desired wavelength, and calculations indicate that a conversion efficiency of 6% could ultimately be realized.

Knowing the size, structure, and interaction forces of nanoparticles in solution is critical to understanding their behavior under realistic conditions. The authors demonstrate a near-field optical technique to simultaneously determine all of these properties. This approach could be broadly useful in applications related to biophysics, colloid and materials research, and pharmacology.

The spin field-effect transistor (spin-FET) is the ultimate spintronic device, and the ultimate issue for spin-FET technology is realizing a high magnetoresistance (MR) ratio in a ferromagnet/semiconductor/ferromagnet sandwich. The authors succeed in fabricating fully epitaxial Fe/GaO${}_x$/Fe magnetic tunnel junctions with MR ratios up to 92% at room temperature—a milestone in the development of spin-FETs in a vertical, rather than planar, configuration.

Incurable neurological disorders such as Alzheimer’s and Parkinson’s diseases presently cannot be diagnosed before symptoms appear. The authors use statistical physics to design and simulate a screening test for early detection based on fluctuations in a small sample’s protein aggregation. This work provides a new approach for the diagnosis of asymptomatic subjects.

Our understanding of charge transport across interfaces needs to be reconsidered at the nanoscale, especially for advanced optoelectronic applications. Systems based on graphene, for example, present highly nonparabolic energy dispersion, for which the Schottky equation fails. The authors formulate a Kane-Schottky scaling relation for current with temperature, bridging the nonrelativistic $T^2$ and relativistic $T^3$ regimes. They show that using incorrect scaling relations to analyze experimental data can produce errors of up to two orders of magnitude.

Realistically simulating a quasi-one-dimensional nanostructure, such as a nanowire, subject to an arbitrary combination of bending, twisting, and stretching is plagued with difficulties. To address this problem, the author presents a powerful and elegant technique based on position-dependent symmetry operations. This approach goes beyond merely improving accuracy and speed of calculations, and enables completely different $kinds$ of modeling.

Graphene could be a wonder material for electronics, due to not just its electrical but also its $thermal$ conductivity, to help keep nanodevices cool. Laying graphene on a substrate tends to spoil this terrific property, but the authors find that atop $h$-BN, graphene surprisingly retains 90% of its thermal conductivity, due to polarization of the graphene and thus strong interlayer adhesion. This study highlights the importance of understanding the interlayer interactions of graphene with dielectric materials in devices.

Controlling oxide-silicon semiconductor heterojunctions is a perpetual challenge in engineering electronic devices, including field-effect transistors and solar cells. The authors use advanced microscopy to perform an atom-by-atom deconstruction of the interface between doped zinc oxide and silicon, to elucidate the cause of Schottky barrier height pinning. The cause turns out to be the unexpected segregation of dopant at the interface—a phenomenon that may affect semiconductor heterojunctions generally.

Growing $III-V$ semiconductor alloys like GaN along different crystal directions, to yield either “Ga-polar” or “N-polar” structures, can have a profound effect on optoelectronic device properties—in particular, green emission from LEDs. For example, the authors find that N-polar (In,Ga)N/GaN quantum wells do not exhibit any detectable luminescence, in striking contrast to their Ga-polar counterparts. This is due to a high density of nonradiative defects at the interfaces between wells and barriers. These results point away from N-polar systems for further development of long-wavelength LEDs.

Recent efforts in the area of wireless power transmission have focused on the nonradiative near field (nonresonant and resonant inductive power transfer) and the far field. The authors propose wireless power transfer in the radiative near field using Bessel beams, robust electromagnetic fields that are diffractionless and self-healing if interrupted. Analysis of coupled antennae that can generate Bessel beams shows a variety of unique properties, thus laying the foundation for this mode of power transfer.