Pair-density-wave and s±ids\pm \mathrm{i}d superconductivity in a strongly coupled, lightly doped Kondo insulator

We investigate the large Kondo coupling limit of the Kondo-Heisenberg model on one- and two-dimensional lattices. Focusing on the possible superconducting states when slightly doping the Kondo insulator state, we identify different pairing modes to be most stable in different parameter regimes. Possibilities include uniform s-wave, pair-density-wave with momentum $\pi$ (in both one and two dimensions) and uniform $s\pm \mathrm{i}d_{x^2-y^2}$-wave (in two dimensions). We attribute these exotic pairing states to the presence of various pair-hopping terms with a "wrong" sign in the effective model, a mechanism that is likely universal for inducing pairing states with spatially modulated pair wavefunctions

Boosting with an aerosolized Ad5-nCoV elicited robust immune responses in inactivated COVID-19 vaccines recipients

IntroductionThe SARS-CoV-2 Omicron variant has become the dominant SARS-CoV-2 variant and exhibits immune escape to current COVID-19 vaccines, the further boosting strategies are required.MethodsWe have conducted a non-randomized, open-label and parallel-controlled phase 4 trial to evaluate the magnitude and longevity of immune responses to booster vaccination with intramuscular adenovirus vectored vaccine (Ad5-nCoV), aerosolized Ad5-nCoV, a recombinant protein subunit vaccine (ZF2001) or homologous inactivated vaccine (CoronaVac) in those who received two doses of inactivated COVID-19 vaccines. ResultsThe aerosolized Ad5-nCoV induced the most robust and long-lasting neutralizing activity against Omicron variant and IFNg T-cell response among all the boosters, with a distinct mucosal immune response. SARS-CoV-2-specific mucosal IgA response was substantially generated in subjects boosted with the aerosolized Ad5-nCoV at day 14 post-vaccination. At month 6, participants boosted with the aerosolized Ad5-nCoV had remarkably higher median titer and seroconversion of the Omicron BA.4/5-specific neutralizing antibody than those who received other boosters. DiscussionOur findings suggest that aerosolized Ad5-nCoV may provide an efficient alternative in response to the spread of the Omicron BA.4/5 variant.Clinical trial registrationhttps://www.chictr.org.cn/showproj.html?proj=152729, identifier ChiCTR2200057278

Quantum Carrier Reinvestment-Induced Ultrahigh and Broadband Photocurrent Responses in Graphene–Silicon Junctions

In an earlier work, we had reported a method that enables graphene–silicon junctions to display exceptionally high <i>photovoltaic</i> responses, exceeding 10⁷ V/W. Using a completely different method that has recently been reported to result in ultrahigh gain, we now show that these junctions can also demonstrate giant <i>photocurrent</i> responsivities that can approach ∼10⁷ A/W. Together, these mechanisms enable graphene–silicon junctions to be a dual-mode, broad-band, scalable, CMOS-compatible, and tunable photodetector that can operate either in photovoltage or photocurrent modes with ultrahigh responsivity values. We present detailed validation of the underlying mechanism (which we call Quantum Carrier Reinvestment, or QCR) in graphene–silicon junctions. In addition to ultrasensitive photodetection, we present QCR photocurrent spectroscopy as a tool for investigating spectral recombination dynamics at extremely low incident powers, a topic of significant importance for optoelectronic applications. We show that such spectroscopic studies can also provide a direct measure of photon energy values associated with various allowed optical transitions in silicon, again an extremely useful technique that can in principle be extended to characterize electronic levels in arbitrary semiconductors or nanomaterials. We further show the significant impact that underlying substrates can have on photocurrents, using QCR-photocurrent mapping. Contrary to expectations, QCR-photocurrents in graphene on insulating SiO₂ substrates can be much higher than its intrinsic photocurrents, and even larger than QCR-photocurrents obtained in graphene overlaying semiconducting or metallic substrates. These results showcase the vital role of substrates in photocurrent measurements in graphene or potentially in other similar materials which have relatively high carrier mobility values

Kinetics of alkali-based photocathode degradation

We report on a kinetic model that describes the degradation of the quantum efficiency (QE) of Cs3Sb and negative electron affinity (NEA) GaAs photocathodes under UHV conditions. In addition to the generally accepted irreversible chemical change of a photocathode’s surface due to reactions with residual gases, such as O2, CO2, and H2O, the model incorporates an intermediate reversible physisorption step, similar to Langmuir adsorption. This intermediate step is needed to satisfactorily describe the strongly non-exponential QE degradation curves for two distinctly different classes of photocathodes –surface-activated and “bulk,” indicating that in both systems the QE degradation results from surface damage. The recovery of the QE upon improvement of vacuum conditions is also accurately predicted by this model with three parameters (rates of gas adsorption, desorption, and irreversible chemical reaction with the surface) comprising metrics to better characterize the lifetime of the cathodes, instead of time-pressure exposure expressed in Langmuir units

Graphene as a Massless Electrode for Ultrahigh-Frequency Piezoelectric Nanoelectromechanical Systems

Designing “ideal electrodes” that simultaneously guarantee low mechanical damping and electrical loss as well as high electromechanical coupling in ultralow-volume piezoelectric nanomechanical structures can be considered to be a key challenge in the NEMS field. We show that mechanically transferred graphene, floating at van der Waals proximity, closely mimics “ideal electrodes” for ultrahigh frequency (0.2 GHz < <i>f</i>₀ < 2.6 GHz) piezoelectric nanoelectromechanical resonators with negligible mechanical mass and interfacial strain and perfect radio frequency electric field confinement. These unique attributes enable graphene-electrode-based piezoelectric nanoelectromechanical resonators to operate at their theoretically “unloaded” frequency-limits with significantly improved electromechanical performance compared to metal-electrode counterparts, despite their reduced volumes. This represents a spectacular trend inversion in the scaling of piezoelectric electromechanical resonators, opening up new possibilities for the implementation of nanoelectromechanical systems with unprecedented performance

Large-Area Synthesis of Graphene on Palladium and Their Raman Spectroscopy

We present a detailed investigation of the nucleation sites, growth, and morphology of large-area graphene samples synthesized via chemical vapor deposition (CVD) on bulk palladium substrates. The CVD chamber was systematically controlled over a large range of growth temperatures and durations, and the nature of graphene growth under these conditions was thoroughly investigated using a combination of scanning electron microscopy and a statistical analysis of >500 Raman spectra. Graphene growth was found to initiate at ∼825 °C, above which the growth rate increased rapidly. At <i>T</i> = 1000 °C, defect-free high-quality graphene was found to grow at an unprecedented rate of tens of micrometers per second, orders of magnitude faster than past reports on Cu- or Ni-based growth, thus leading to macroscopic coverage of the substrate within seconds of growth initiation. By arresting the growth at lower temperatures, we found that graphene nanoislands preferred to nucleate at very specific positions close to terrace edges and step inner edges. Evidence of both epitaxial and self-limiting growth was found. Along with monolayer graphene, both Bernal and turbostratic multilayer graphene could be obtained. A detailed evolution of the different types of graphene, as a function of both growth temperature and duration, has been presented. From these, optimal growth conditions for any chosen type of graphene sample can be inferred

Colloidal Synthesis and Optical Properties of Cs₂CuCl₄ Nanocrystals

Lead-free copper halide perovskite nanocrystals (NCs) are emerging materials with excellent photoelectric properties. Herein, we present a colloidal synthesis route for orthorhombic Cs2CuCl4 NCs with a well-defined cubic shape and an average diameter of 24 ± 2.1 nm. The Cs2CuCl4 NCs exhibited bright, deep blue photoluminescence, which was attributed to the Cu(II) defects. In addition, passivating the Cs2CuCl4 NCs by Ag+ could effectively improve the photoluminescence quantum yield (PLQY) and environmental stability