Width-tuned magnetic order oscillation on zigzag edges of honeycomb nanoribbons

Quantum confinement and interference often generate exotic properties in nanostructures. One recent highlight is the experimental indication of a magnetic phase transition in zigzag-edged graphene nanoribbons at the critical ribbon width of about 7 nm [G. Z. Magda et al., Nature \textbf{514}, 608 (2014)]. Here we show theoretically that with further increase in the ribbon width, the magnetic correlation of the two edges can exhibit an intriguing oscillatory behavior between antiferromagnetic and ferromagnetic, driven by acquiring the positive coherence between the two edges to lower the free energy. The oscillation effect is readily tunable in applied magnetic fields. These novel properties suggest new experimental manifestation of the edge magnetic orders in graphene nanoribbons, and enhance the hopes of graphene-like spintronic nanodevices functioning at room temperature.Comment: 22 pages, 9 figure

ZZ boson radiative decays to a SS-wave quarkonium at NNLO and NLL accuracy

Within the framework of nonrelativistic QCD (NRQCD) factorization formalism, we compute QCD next-to-next-to-leading order (NNLO) corrections to the helicity amplitudes as well as the decay width of $Z\to H+\gamma$, where $H$ can be $\eta_Q (Q=c,b), J/\psi$, or $\Upsilon$. In addition, we resum the next-to-leading logarithms (NLL) of ${m_Z^2}/{m_Q^2}$ to all orders of $\alpha_s$ for the leading-twist helicity amplitude by employing the light-cone factorization approach. It is worth mentioning that we obtain the analytic expressions of the truncated NLL at $\alpha_s^2$. We find that the $\mathcal{O}(\alpha_s)$ corrections are around 10\% for $\eta_c$ and $\Upsilon$ productions, however insignificant for $J/\psi$ and $\eta_b$ productions. The $\mathcal{O}(\alpha_s^2)$ corrections are moderate for charmonium production, while very small for bottomonium production. Moreover, it is found that the NLL resummation can considerably alter the NRQCD prediction, especially for $J/\psi$ production. Combining the NRQCD and light-cone computation, we make phenomenological predictions on the decay widths and branching fractions. In addition, we investigate the dependence of the theoretical results on the heavy quark mass, and find the branching fraction of $Z\to H+\gamma$ monotonically decreases as $m_Q$ increases.Comment: 21 pages, 2 figures, 3 tables. correct typos, add the comparison with LC models, match the published version in PRD. arXiv admin note: text overlap with arXiv:2208.1011

Effects of Sintering Conditions on Microstructure Changes of Wood-Ceramics Impregnated with Low-Molecular-Weight Phenol-Formaldehyde Resin

The microstructure of a new type of wood-ceramics made from poplar fiber impregnated with low-molecular-weight phenol-formaldehyde (PF) resin under atmospheric pressure was studied under changing sintering conditions. X-ray diffraction analysis indicated that the d002 value was reduced with increasing sintering temperature. The wood-ceramic structure also became more uniform and orderly, but still was nongraphitic carbon. Scanning electron microscopy showed that the pore structure partially retained the microstructural characteristics of wood fiber, and a graphitic phase was formed with increased sintering temperature and longer holding time. All analyses showed PF resin molecular weight had little impact on phase composition and graphitization. The apparent specific gravity of woodceramics increased as sintering temperature increased to 1200°C but decreased as temperature rose further. Specific surface area and apparent porosity were increased with higher sintering temperature, greater sintering rates, and longer holding times. In addition, specific surface area was also affected by the molecular weight of PF resin and the impregnation method, in which low-molecular-weight resin increased the specific surface area