ABSTRACT
In developing nonvolatile valleytronic devices, ferromagnetic (FM) ferrovalley semiconductors are critically needed due to the existence of spontaneous valley polarization. At present, however, the known real materials have various drawbacks towards practical applications, including the in-plane FM ground state, low Curie temperature (TC), small valley polarization, narrow energy window with clean polarized valley, and indirect bandgap. From first-principles calculations, here we predict anideal ferrovalley semiconductor, honeycomb LaH2monolayer (ML), whose intrinsic properties can overcome all these shortcomings. We demonstrate that LaH2ML, having satisfied structural stability, is a FM half-semiconducting electrene (La3+2H-â e-) with its magnetic moments localized at the lattice interstitial sites rather than La atoms. At the same time, LaH2ML holds the following desired attributes: a robust out-of-plane FM ground state with a highTC(334 K), a sizable valley polarization (166 meV), a wide energy window (137 meV) harboring clean single-valley carriers, and a direct bandgap. These results identify a much needed ideal ferrovalley semiconductor candidate, holding the promising application potential in valleytronics and spintronics devices.
ABSTRACT
Recently, a new class of 2D Dirac materials, spin-valley-coupled Dirac semimetals (svc-DSMs), was proposed in strained SbAsX2 monolayers (MLs) and transition metal dichalcogenide-supported graphene. Owing to the superb properties, including Dirac spin-valley Hall effect and dissipationless transport, svc-DSMs provide an ideal platform for exploring the integration of Dirac physics, spintronics and valleytronics. However, the predicted candidate materials are all extrinsic, requiring tensile strain or proximity effect. Using first-principles calculations, herein we identify that strain-free BrBiAsCl ML is an intrinsic svc-DSM that is located at the boundary between 2D trivial insulators and topological insulators owing to the balance between spin-orbit coupling (SOC) and the built-in polarized vertical electric field. Under inversion asymmetry, the strong SOC in BrBiAsCl ML induces giant spin-splittings in both the uppermost valence band and the lowermost conduction band, rendering a nearly closed bulk gap and the formation of a spin-valley-dependent Dirac cone. Remarkably, such an svc-DSM state can be well preserved in BrBiAsCl ML when supported on a proper substrate, which is indispensable for the application of svc-DSMs in devices.
ABSTRACT
A novel concept and theory of moving reaction boundary (MRB) retardation signal (RMRB) was advanced for determination of total protein content via MRB electrophoretic titration (MRBET). The theoretical results revealed that the retardation extent of boundary displacment, viz., the RMRB value, was as a function of protein content. Thus, the RMRB value of a sample could be used to determine its total protein content according to the relevant calibration curve. To demonstrate the concept and theoretical results, a novel microdevice was designed for the relevant experiments of MRBET. The microdevice has 30 identical work cells, each of which is composed of five ultrashort single microchannels (5 mm). In the microdevice, fluorescein isothiocyanate (FITC) was used to denote MRB motion and RMRB value for the first time, the polyacrylamide gel (PAG) containing protein sample was photopolymerized in microchannels, and the MRB was created with acid or alkali and target protein sample. As compared to the classic Kjeldahl method and conventional MRBET performed in glass tube, the developed titration chip has the following merits: good sensitivity (0.3-0.4 µg/mL vs 150-200 µg/mL of protein concentration, 0.6-0.8 ng vs 30-2000 µg of absolute protein content), rapid analysis (20-60 s vs 15-200 min), and portable low-power (15 V vs 200 V).
