Electric-field Control of Magnetism with Emergent Topological Hall Effect in SrRuO3 through Proton Evolution

Ionic substitution forms an essential pathway to manipulate the carrier density and crystalline symmetry of materials via ion-lattice-electron coupling, leading to a rich spectrum of electronic states in strongly correlated systems. Using the ferromagnetic metal SrRuO3 as a model system, we demonstrate an efficient and reversible control of both carrier density and crystalline symmetry through the ionic liquid gating induced protonation. The insertion of protons electron-dopes SrRuO3, leading to an exotic ferromagnetic to paramagnetic phase transition along with the increase of proton concentration. Intriguingly, we observe an emergent topological Hall effect at the boundary of the phase transition as the consequence of the newly-established Dzyaloshinskii-Moriya interaction owing to the breaking of inversion symmetry in protonated SrRuO3 with the proton compositional film-depth gradient. We envision that electric-field controlled protonation opens a novel strategy to design material functionalities

Effect of lattice mismatch on film morphology of the quasi-one dimensional conductor K0.3MoO3

High quality epitaxial thin films of the quasi-one dimensional conductor K0.3MoO3 have been successfully grown on SrTiO3(100), SrTiO3(110), and SrTiO3(510) substrates via pulsed laser deposition. Scanning electron microscopy revealed quasi-one dimensional rod-shaped structures parallel to the substrate surface, and the crystal structure was verified by using X-ray diffraction. The temperature dependence of the resistivity for the K0.3MoO3 thin films demonstrates a metal-to-semiconductor transition at about 180 K. Highly anisotropic resistivity was also observed for films grown on SrTiO3(510).Published versio

Reversible manipulation of the magnetic state in SrRuO3 through electric-field controlled proton evolution

Ionic substitution forms an essential pathway to manipulate the structural phase, carrier density and crystalline symmetry of materials via ion-electron-lattice coupling, leading to a rich spectrum of electronic states in strongly correlated systems. Using the ferromagnetic metal SrRuO3 as a model system, we demonstrate an efficient and reversible control of both structural and electronic phase transformations through the electric-field controlled proton evolution with ionic liquid gating. The insertion of protons results in a large structural expansion and increased carrier density, leading to an exotic ferromagnetic to paramagnetic phase transition. Importantly, we reveal a novel protonated compound of HSrRuO3 with paramagnetic metallic as ground state. We observe a topological Hall effect at the boundary of the phase transition due to the proton concentration gradient across the film-depth. We envision that electric-field controlled protonation opens up a pathway to explore novel electronic states and material functionalities in protonated material systems

Fewer new species colonize at low frequency N addition in a temperate grassland

Biologically reactive nitrogen (Nr) enrichment threatens biodiversity in diverse ecosystems. Previous controlled N addition experiments may overestimate the effects of atmospheric Nr deposition on the rate of species loss, as it has been found that low frequency Nr additions, as used in traditional studies, lead to more rapid biodiversity loss. It remains unclear, however, whether the colonization of new species (gain) or extinction of old species (loss) is the cause of this difference. By independently manipulating the frequency (twice vs. monthly additions year(-1)) and the rate (from 0 to 50g Nm(-2)year(-1)) of NH4NO3 inputs for six years in a temperate grassland of northern China, we aimed to examine the contribution of gain and loss of species to the reduction in species richness under different regimes of Nr inputs. Results showed that the gain of new species was higher at a high frequency of N addition than that at a low addition frequency, while loss of existing species was similar between the two frequencies of N addition. The number of new species gained decreased and old species lost increased with the increasing rate of Nr addition at both annual and five-year intervals. Cumulative gain of new species was negatively correlated with soil acidification, ammonium concentration and community biomass accumulation, whereas cumulative loss of old species was positively correlated with these variables. Our results revealed lower new species colonization results in lower species richness at low frequency of Nr addition. Findings from this study highlight the important role of N addition frequency in regulating the effects of Nr addition on community dynamics. To assess the effects of atmospheric Nr deposition on ecosystem structure and functioning, it is necessary to assess not only the dose but also the frequency of N addition

Effects of the frequency and the rate of N enrichment on community structure in a temperate grassland

Aims Nitrogen (N) enrichment caused by human activities threatens biodiversity and alters plant community composition and structure. It has been found that heavy and infrequent N inputs may overestimate species extinction, but it remains unclear whether plant community structure will equally respond to frequent reactive N enriched conditions. Methods We independently manipulated the rates and the frequencies of N addition in a temperate steppe, northern China, between 2008 and 2013. Important Findings We found that plant community structure changes, measured by 'Euclidean distance' involving species richness, composition and productivity, were significantly positively related to increasing N enrichment rates rather than frequencies. Changes in aboveground net primary productivity (ANPP), plant species richness and shifts in dominant species were observed. Community ANPP increased with N enrichment, whereas species richness reduced. The frequency of N enrichment increased species richness but had no impacts on community ANPP and the relative ANPP of the two dominant species, C-3 perennial bunchgrass Stipa grandis and C-3 perennial rhizome grass Leymus chinensis. The ANPP and relative ANPP of the two dominant species were significantly negatively correlated with each other. Moreover, changes in the relative ANPP of S. grandis was negatively associated with the changes in community structure. After 5 years' treatment, direct influence of the frequency of N enrichment on plant community structure was not observed, but the effects of the rate of N enrichment were apparent. Our results suggested that further study in various ecosystems and with long-term and well-controlled comparisons the frequency vs. the rate of N enrichment may still be needed

Environmental filtering rather than phylogeny determines plant leaf size in three floristically distinctive plateaus

Leaf is essential for plant growth and development; however, the relative importance of environmental filtering and phylogeny in determining leaf size across different spatial scales in grassland ecosystems remains poorly explored. We used transect methodology to explore the spatial variation in leaf size and its underlying mechanisms in grasslands along three topographically and floristically distinctive plateaus in northern China. We measured leaf size of a total of 1192 grassland species in the Tibetan Plateau (TP, temperature limited), Loess Plateau (LP, soil-nutrient limited), and Mongolia Plateau (MP, precipitation limited) along three transects encompassing meadow, typical, and desert steppes. Leaf size ranged from 0.01 to 258.16 cm2, with an average of 5.54 cm2. The smallest leaves were measured in the TP. At the vegetation association level, the largest leaves were present in the meadow steppe, followed by those in typical and desert steppes, irrespective of the plateau. Unexpectedly, phylogeny had a negligible effect on the spatial variation in leaf size in the grasslands. Leaf size was positively correlated with growing-season temperature and precipitation but negatively correlated with ultraviolet (UV) radiation, suggesting that environmental filtering plays a more important role in affecting leaf size than phylogeny. Furthermore, leaf size in the TP and MP was mainly affected by precipitation and UV radiation, respectively, whereas that in the LP was affected by temperature, precipitation, soil nutrients and UV light. Specifically, our results underscored the importance of environmental filtering rather than phylogeny in determining plant leaf size and shed light on the unexpected role of UV radiation in contributing to leaf size variations in these plateaus. Our study provides novel insights into the response of plants to global change, especially in plateaus, alpine zone, and high-latitude areas

Tuning the electronic properties of epitaxial strained CaFeO3−δ thin films

Strain engineering of transition metal oxides due to their desirable properties has long been a focal point in both physics and material sciences. Here, we investigate the strain dependence of electronic and optical properties of the high valence iron-based perovskite CaFeO3d. Using substrates with various lattice constants, we achieve a wide range of tunable epitaxial strain states in CaFeO3d thin films ranging from compressive 0.37% to tensile 3.58%. Electrical transport and optical absorption measurements demonstrate a distinct strain-dependent behavior, in which larger tensile strain leads to higher electrical resistivity and a larger optical bandgap. We attribute these modulations to tensile strain suppressed p-d hybridization in CaFeO3d, as evidenced by soft X-ray absorption spectra measurements