Exciton-coupled coherent magnons in a 2D semiconductor.

The recent discoveries of two-dimensional (2D) magnets1-6 and their stacking into van der Waals structures7-11 have expanded the horizon of 2D phenomena. One exciting application is to exploit coherent magnons12 as energy-efficient information carriers in spintronics and magnonics13,14 or as interconnects in hybrid quantum systems15-17. A particular opportunity arises when a 2D magnet is also a semiconductor, as reported recently for CrSBr (refs. 18-20) and NiPS3 (refs. 21-23) that feature both tightly bound excitons with a large oscillator strength and potentially long-lived coherent magnons owing to the bandgap and spatial confinement. Although magnons and excitons are energetically mismatched by orders of magnitude, their coupling can lead to efficient optical access to spin information. Here we report strong magnon-exciton coupling in the 2D A-type antiferromagnetic semiconductor CrSBr. Coherent magnons launched by above-gap excitation modulate the exciton energies. Time-resolved exciton sensing reveals magnons that can coherently travel beyond seven micrometres, with a coherence time of above five nanoseconds. We observe these exciton-coupled coherent magnons in both even and odd numbers of layers, with and without compensated magnetization, down to the bilayer limit. Given the versatility of van der Waals heterostructures, these coherent 2D magnons may be a basis for optically accessible spintronics, magnonics and quantum interconnects.

All-Sputtered, Superior Power Density Thin-Film Solid Oxide Fuel Cells with a Novel Nanofibrous Ceramic Cathode.

Thin film solid oxide fuel cells (TF-SOFCs) are attracting attention due to their ability to operate at comparatively lower temperatures (400-650 °C) that are unattainable for conventional anode-supported SOFCs (650-800 °C). However, limited cathode performance and cell scalability remain persistent issues. Here, we report a new approach of fabricating yttria-stabilized zirconia (YSZ)-based TF-SOFCs via a scalable magnetron sputtering process. Notable is the development and deposition of a porous La0.6Sr0.4Co0.2Fe0.8O2.95(LSCF)-based cathode with a unique fibrous nanostructure. This all-sputtered cell shows an open-circuit voltage of ∼1.0 V and peak power densities of ∼1.7 and ∼2.5 W/cm2 at 600 and 650 °C, respectively, under hydrogen fuel and air along with showing stable performance in short-term testing. The power densities obtained in this work are the highest among YSZ-based SOFCs at these low temperatures, which demonstrate the feasibility of fabricating exceptionally high-performance TF-SOFC cells with distinctive dense or porous nanostructures for each layer, as desired, by a sputtering process. This work illustrates a new, potentially low-cost, and scalable platform for the fabrication of next-generation TF-SOFCs with excellent power output and stability.

Ruthenium doping in the MoS2/AB heterostructure for the hydrogen evolution reaction in acidic media.

Electrocatalyst design is an important approach to prompt the commercialization of water electrolysis technologies. In this work, a ruthenium doped MoS2/AB heterostructure is synthesized as an electrocatalyst for the hydrogen evolution reaction (HER) through hydrothermal and annealing processes. The physical-chemical characterization studies show that the MoS2/AB heterostructure and the incorporation of Ru effectively induce a phase transition from 2H to 1T-MoS2. The as-prepared Ru-MoS2/AB exhibits an excellent HER performance with a very low overpotential of 13 mV at 10 mA cm-2 and a Tafel slope of 31 mV dec-1 in 0.5 M H2SO4, remarkably higher than those of Pt/C (overpotential of 28 mV at 10 mA cm-2, 41 mV dec-1). Density functional theory calculations suggest that the H absorption on Ru bonding to S exhibits a rather low binding energy (-0.22 eV), indicating the optimum active sites of Ru near S for HER. Significantly, the Ru-MoS2/AB also demonstrates high stability under long-term discharge and elevated temperature conditions. These results suggest that the as-prepared Ru-MoS2/AB can be a promising alternative to Pt/C for water electrolysis, due to its high HER activity, easy synthesis, and good stability.

Hybrid spin Hall nano-oscillators based on ferromagnetic metal/ferrimagnetic insulator heterostructures.

Spin-Hall nano-oscillators (SHNOs) are promising spintronic devices to realize current controlled GHz frequency signals in nanoscale devices for neuromorphic computing and creating Ising systems. However, traditional SHNOs devices based on transition metals have high auto-oscillation threshold currents as well as low quality factors and output powers. Here we demonstrate a new type of hybrid SHNO based on a permalloy (Py) ferromagnetic-metal nanowire and low-damping ferrimagnetic insulator, in the form of epitaxial lithium aluminum ferrite (LAFO) thin films. The superior characteristics of such SHNOs are associated with the excitation of larger spin-precession angles and volumes. We further find that the presence of the ferrimagnetic insulator enhances the auto-oscillation amplitude of spin-wave edge modes, consistent with our micromagnetic modeling. This hybrid SHNO expands spintronic applications, including providing new means of coupling multiple SHNOs for neuromorphic computing and advancing magnonics.

Ultra-thin lithium aluminate spinel ferrite films with perpendicular magnetic anisotropy and low damping.

Ultra-thin films of low damping ferromagnetic insulators with perpendicular magnetic anisotropy have been identified as critical to advancing spin-based electronics by significantly reducing the threshold for current-induced magnetization switching while enabling new types of hybrid structures or devices. Here, we have developed a new class of ultra-thin spinel structure Li0.5Al1.0Fe1.5O4 (LAFO) films on MgGa2O4 (MGO) substrates with: 1) perpendicular magnetic anisotropy; 2) low magnetic damping and 3) the absence of degraded or magnetic dead layers. These films have been integrated with epitaxial Pt spin source layers to demonstrate record low magnetization switching currents and high spin-orbit torque efficiencies. These LAFO films on MGO thus combine all of the desirable properties of ferromagnetic insulators with perpendicular magnetic anisotropy, opening new possibilities for spin based electronics.

A Wearable Colorimetric Dosimeter to Monitor Sunlight Exposure.

The personal ultraviolet (UV) dosimeter is a useful measurement tool to prevent UV induced dermal damages; however, conventional digital dosimeters are either bulky or require external power sources. Here, a wearable, colorimetric UV film dosimeter that provides color transition, from purple to transparent, is reported to indicate the UV dose. The film dosimeter is made of a purple photodegradable dye ((2Z,6Z)-2,6-bis(2-(2,6-diphenyl-4H-thiopyran-4-ylidene)ethylidene)cyclohexanone or DTEC) blended in low density polyethylene film. The DTEC film discolored 3.3 times more under the exposure of UV light (302 nm) than visible light (543 nm), and a UV bandpass filter is developed to increase this selectivity to UV light. The DTEC film completely discolors to transparency in 2 h under an AM 1.5 solar simulator, suggesting the potential as an indicator for individuals with types I-VI skin to predict interventions to avoid sunburn. Finally, the DTEC film is integrated with the UV bandpass filter on a wristband to function as a wearable dosimeter for low cost and convenient monitoring of sunlight exposure.