Current imaging via scanning diamond magnetometry is a valuable tool in the study of transport phenomena, due to its applicability over a wide temperature range, but its sensitivity for resolving subtle features and small currents has remained limited. By implementing ac measurement protocols and phase-unwrapping schemes, the authors detect currents below 1 µA in bilayer graphene, and resolve minute variations on top of background signals. They also observe current-density variations due to a varying background potential, and discuss measurement-induced back-action and how to avoid it. These advances establish scanning diamond magnetometry as an excellent option for current imaging.

Characterizing magnetic textures is important for applications in stochastic computing and memory devices based on magnetic skyrmions. Knowing the exact number of skyrmions is essential for these tasks, yet this count is particularly difficult to determine when dealing with quickly moving skyrmions at nonzero temperatures, where only time-averaged, smeared results are available. The present study uses machine-learning techniques to solve this problem successfully, to the benefit of future investigations in spintronic computation and memory applications.

Metamaterials continue to be conceptually intriguing for the manipulation of propagating waves. However, preventing low-frequency wave propagation proves to be challenging, due to limited metamaterial dimensions and mass. This study focuses on a metamaterial lattice featuring geometrically nonlinear behavior that can lead to negative stiffness, aimed at overcoming the requirement of large mass for low-frequency vibration attenuation. This approach can find application in structural engineering to protect against low-frequency excitations—such as earthquakes.

Terahertz technology suffers from a lack of efficient emitters, but dc excitation of plasma waves in two-dimensional electron systems (2DESs) is a promising solution. Ultrahigh-mobility 2DESs would help to avoid the Ohmic losses that have plagued the implementation of such devices, but reduced Ohmic loss comes at the cost of damping via viscous loss. The authors exploit a recently developed perturbative technique to develop a systematic treatment of viscosity-induced plasmon damping, and provide a powerful tool for optimizing plasmonic resonators.

Quasi-Fermi levels (QFLs) have become a canonical concept in semiconductor device modeling. However, a global model to cover both unipolar and ambipolar transport modes of two-dimensional field-effect transistors (2D FETs) based on QFLs is still needed, as it is challenging to capture quantitatively the effect of QFL splitting on transport. This work establishes a theoretical platform to account for that effect: the quasi-Fermi-level phase space (QFLPS). With QFLPS a unified picture of unipolar and ambipolar transport is drawn, the working modes of 2D FETs acquire more intuitive physical interpretations, and many valuable outcomes for device modeling and circuit design are realized.

The emergent topological semimetals have received considerable attention for developing innovative devices, mainly due to their novel topological electronic properties with high robustness against external perturbations. Progress has been hindered, though, due to a lack of tunability. Here the authors address this challenge by constructing a field-effect device based on thin flakes of tellurium, a semiconductor with a chiral Weyl node. In this device, the conducting and topological states can be simultaneously switched electrostatically, yielding giant modulations of both channel conductivity and chiral-anomaly-induced magnetoresistance.

High-density spintronic applications such as digital memory require strong perpendicular magnetic anisotropy (PMA), to maintain data stability above room temperature, which so far has been beyond the reach of stacked van der Waals ferromagnets. Here the authors demonstrate that the interlayer exchange coupling in a magnetic multilayer can effectively tune the Curie temperature and PMA of sandwiched two-dimensional (2D) Fe${}_3$GeTe${}_2$. The successful realization of room-temperature 2D ferromagnets bearing fully nonvolatile out-of-plane spin information could bring 2D spintronic applications to reality.

The spontaneous alignment of molecular dipoles that occurs in many organic light-emitting diodes (OLEDs) is known to blunt their performance, but is not easy to control within a given device stack. This study shows that coevaporating a small amount of polyethylene in the electron-transport layer of an OLED dramatically reduces the spontaneous orientational polarization, leading to increased device efficiency and lifetime due to decreased exciton-polaron annihilation in the emissive layer. This result highlights the potential of semiconductor dilution to improve OLED performance, and provides a new means to understand exciton-polaron-driven degradation in blue OLEDs.

Current imaging via scanning diamond magnetometry is a valuable tool in the study of transport phenomena, due to its applicability over a wide temperature range, but its sensitivity for resolving subtle features and small currents has remained limited. By implementing ac measurement protocols and phase-unwrapping schemes, the authors detect currents below 1 µA in bilayer graphene, and resolve minute variations on top of background signals. They also observe current-density variations due to a varying background potential, and discuss measurement-induced back-action and how to avoid it. These advances establish scanning diamond magnetometry as an excellent option for current imaging.

Characterizing magnetic textures is important for applications in stochastic computing and memory devices based on magnetic skyrmions. Knowing the exact number of skyrmions is essential for these tasks, yet this count is particularly difficult to determine when dealing with quickly moving skyrmions at nonzero temperatures, where only time-averaged, smeared results are available. The present study uses machine-learning techniques to solve this problem successfully, to the benefit of future investigations in spintronic computation and memory applications.

Metamaterials continue to be conceptually intriguing for the manipulation of propagating waves. However, preventing low-frequency wave propagation proves to be challenging, due to limited metamaterial dimensions and mass. This study focuses on a metamaterial lattice featuring geometrically nonlinear behavior that can lead to negative stiffness, aimed at overcoming the requirement of large mass for low-frequency vibration attenuation. This approach can find application in structural engineering to protect against low-frequency excitations—such as earthquakes.

Terahertz technology suffers from a lack of efficient emitters, but dc excitation of plasma waves in two-dimensional electron systems (2DESs) is a promising solution. Ultrahigh-mobility 2DESs would help to avoid the Ohmic losses that have plagued the implementation of such devices, but reduced Ohmic loss comes at the cost of damping via viscous loss. The authors exploit a recently developed perturbative technique to develop a systematic treatment of viscosity-induced plasmon damping, and provide a powerful tool for optimizing plasmonic resonators.

Quasi-Fermi levels (QFLs) have become a canonical concept in semiconductor device modeling. However, a global model to cover both unipolar and ambipolar transport modes of two-dimensional field-effect transistors (2D FETs) based on QFLs is still needed, as it is challenging to capture quantitatively the effect of QFL splitting on transport. This work establishes a theoretical platform to account for that effect: the quasi-Fermi-level phase space (QFLPS). With QFLPS a unified picture of unipolar and ambipolar transport is drawn, the working modes of 2D FETs acquire more intuitive physical interpretations, and many valuable outcomes for device modeling and circuit design are realized.

The emergent topological semimetals have received considerable attention for developing innovative devices, mainly due to their novel topological electronic properties with high robustness against external perturbations. Progress has been hindered, though, due to a lack of tunability. Here the authors address this challenge by constructing a field-effect device based on thin flakes of tellurium, a semiconductor with a chiral Weyl node. In this device, the conducting and topological states can be simultaneously switched electrostatically, yielding giant modulations of both channel conductivity and chiral-anomaly-induced magnetoresistance.