Band engineering of a magnetic thin film rare earth monopnictide

Realizing quantum materials in few atomic layer morphologies is a key to both observing and controlling a wide variety of exotic quantum phenomena. This includes topological electronic materials, where the tunability and dimensionality of few layer materials have enabled the detection of $Z_2$, Chern, and Majorana phases. Here, we report the development of a platform for thin film correlated, topological states in the magnetic rare-earth monopnictide ($RX$) system GdBi synthesized by molecular beam epitaxy. This material is known from bulk single crystal studies to be semimetallic antiferromagnets with Neel temperature $T_N =$ 28 K and is the magnetic analog of the non-$f$-electron containing system LaBi proposed to have topological surface states. Our transport and magnetization studies of thin films grown epitaxially on BaF$_2$ reveal that semimetallicity is lifted below approximately 8 crystallographic unit cells while magnetic order is maintained down to our minimum thickness of 5 crystallographic unit cells. First-principles calculations show that the non-trivial topology is preserved down to the monolayer limit, where quantum confinement and the lattice symmetry give rise to a $C=2$ Chern insulator phase. We further demonstrate the stabilization of these films against atmospheric degradation using a combination of air-free buffer and capping procedures. These results together identify thin film $RX$ materials as potential platforms for engineering topological electronic bands in correlated magnetic materials

Strategies on Poisonous Plants Problem in China

Poisonous plants are widely distributed on large areas of native grasslands of China, causing livestock poisoning and grassland degradation, which severely impacts the development of animal husbandry. Of the almost 300 poisonous species that are responsible for livestock losses in China, locoweed, drunken horse grass and Langdu cause the greatest impact. Many strategies have been developed to minimise the impact of poisonous plants including the treatment of livestock that have been poisoned, controlling poisonous plants and managing livestock grazing. Both physical and chemical traditional methods are still used to eliminate poisonous plants while biological control using specific insects may eventually be used to control certain species. According to a grassland law, grazing systems (rotational, rest and forbidden grazing) may be applied on dense stands of poisonous plants

Effects of Stocking Rate on the Variability of Ecosystem Productivity in Desert Steppe

Management practices can increase biodiversity and generate corresponding compensatory effects on biomass production, which may reduce inter-annual variability of productivity in some grassland ecosystems. However, it remains unclear how stocking rate influences variability of ecosystem productivity. Four stocking rates were compared in a completely randomized block experiment in the desert steppe of Inner Mongolia, China: non-grazed control (0 sheep/ha/mo), lightly grazed (LG, 0.15 sheep/ha/mo), moderately grazed (MG, 0.30 sheep/ha/mo) and heavily grazed (HG, 0.45 sheep/ha/mo). Aboveground net primary productivity (ANPP) was measured every August for eight consecutive years (2004-2011). ANPP decreased significantly (P \u3c 0.05) with increasing stocking rate. Coefficients of variation for community (CVcomm) in LG and MG were lower than in the control and HG treatments. Coefficients of variation for both species (CVsp) and functional groups (CVPFG) showed logarithmic relationships with relative density (P \u3c 0.05). Thus, both stocking rate and annual precipitation significantly affected the biodiversity and stability of desert steppe in terms of interannual variability of ANPP. As in other grazed systems, our results indicate that grazing management can alter dominant species and functional group components within the grassland community