Electron-phonon coupling and superconductivity in LiB1+x_{1+x}C1−x_{1-x}

By means of the first-principles density-functional theory calculation and Wannier interpolation, electron-phonon coupling and superconductivity are systematically explored for boron-doped LiBC (i.e. LiB$_{1+x}$C$_{1-x}$), with $x$ between 0.1 and 0.9. Hole doping introduced by boron atoms is treated through virtual-crystal approximation. For the investigated doping concentrations, our calculations show the optimal doping concentration corresponds to 0.8. By solving the anisotropic Eliashberg equations, we find that LiB$_{1.8}$C$_{0.2}$ is a two-gap superconductor, whose superconducting transition temperature, T$_c$, may exceed the experimentally observed value of MgB$_2$. Similar to MgB$_2$, the two-dimensional bond-stretching $E_{2g}$ phonon modes along $\Gamma$-$A$ line have the largest contribution to electron-phonon coupling. More importantly, we find that the first two acoustic phonon modes $B_1$ and $A_1$ around the midpoint of $K$-$\Gamma$ line play a vital role for the rise of T$_c$ in LiB$_{1.8}$C$_{0.2}$. The origin of strong couplings in $B_1$ and $A_1$ modes can be attributed to enhanced electron-phonon coupling matrix elements and softened phonons. It is revealed that all these phonon modes couple strongly with $\sigma$-bonding electronic states.Comment: 7 pages, 10 figures, accepted for publication in EP

Neutron diffraction study of the electronic structure of high-T[subscript c] superconductor-related compounds

Neutron diffraction techniques have been used to study the electronic structure of La[subscript]2NiO[subscript]4 and Sr[subscript]2CuO[subscript]2Cl[subscript]2 by measuring the antiferromagnetic form factor of the single-crystal samples at 15 K. The antiferromagnetic form factor was obtained from the integrated intensities of several magnetic reflections. In both cases, the experimentally determined form factor exhibits a plateau at low Q values (up to 3 A[superscript]-1), similar to that observed for La[subscript]2CuO[subscript]4. Detailed modelling of the experimental data of these three compounds suggests that the observed plateau may be accounted for by including the covalency effects in the Ni-O or Cu-O plane. The experimental data are also compared with spin-polarized band calculations

(De-)activating the growth machine for redevelopment: the case of Liede urban village in Guangzhou

This research investigates the mechanism of urban village redevelopment in south China. Through a revised typology of place entrepreneurs based on the growth machine thesis and a case study of Liede village in central Guangzhou, it illustrates how land-based interests embedded in an imbalanced power relationship can (de-)activate urban village redevelopment. The study reveals that while urban villagers, as represented by the village collective, have entrenched interests in the redevelopment process, the city government – as monopolistic land manager and place entrepreneur – plays the deciding role in forging and halting a growth machine geared towards urban village redevelopment. Although developers are also part of the process, the (de-)activation of redevelopment growth machine/coalition in Guangzhou has largely been dominated by the city government. With a comparative view on the original growth machine model, it is hoped that this study would furnish both theoretical and practical thoughts for future research

Food scares and asymmetric price transmission: the case of the pork market in China

This paper investigates the symmetry of impact from three main food scare events on both the upstream and downstream price transmissions in the Chinese pork market through monthly data from 2001 to 2014. Based on a theoretical model, we firstly estimate the VAR systems for pork retail price and price transmissions in different links, and then plot the impulse response function and dynamic multiplier function respectively for endogenous substitute good price and exogenous food scare events. Empirical results indicate the asymmetry of price transmission in the Chinese pork market, and demand and supply shocks from three food scare incidents are found to impact retail price and price transmissions differentially. In addition, shocks from the same incident on price and price transmissions are significantly different. This research provides implications for farmers, business managers and policy makers to make strategies in response to food scare events