Evolution of structural and magnetic properties in Ta/Ni_81Fe_(19) multilayer thin films

The interdiffusion kinetics in short period (12.8 nm) Ta/Ni81Fe19 polycrystalline multilayer films has been investigated and related to the evolution of soft magnetic properties upon thermal annealing in the temperature range 300-600-degrees-C. Small angle x-ray diffraction and transmission electron microscopy were used to estimate the multilayer period. Interdiffusion in the multilayers was directly computed from the decay of the satellites near (000) in a small angle x-ray diffraction spectrum. A kinetic analysis of interdiffusion suggests that grain growth is concurrent with grain boundary diffusion of Ta in Ni81Fe19. The evolution of soft magnetic properties of Ni81Fe19, i.e., lowering of 4piM(s) and increase in coercivity H(c), also lend support to the above analysis

Doping evolution of spin and charge excitations in the Hubbard model

To shed light on how electronic correlations vary across the phase diagram of the cuprate superconductors, we examine the doping evolution of spin and charge excitations in the single-band Hubbard model using determinant quantum Monte Carlo (DQMC). In the single-particle response, we observe that the effects of correlations weaken rapidly with doping, such that one may expect the random phase approximation (RPA) to provide an adequate description of the two-particle response. In contrast, when compared to RPA, we find that significant residual correlations in the two-particle excitations persist up to $40\%$ hole and $15\%$ electron doping (the range of dopings achieved in the cuprates). These fundamental differences between the doping evolution of single- and multi-particle renormalizations show that conclusions drawn from single-particle processes cannot necessarily be applied to multi-particle excitations. Eventually, the system smoothly transitions via a momentum-dependent crossover into a weakly correlated metallic state where the spin and charge excitation spectra exhibit similar behavior and where RPA provides an adequate description.Comment: 5 pages, 4 figures, plus supplementary materia

Doping Evolution of Oxygen K-edge X-ray Absorption Spectra in Cuprate Superconductors

We study oxygen K-edge x-ray absorption spectroscopy (XAS) and investigate the validity of the Zhang-Rice singlet (ZRS) picture in overdoped cuprate superconductors. Using large-scale exact diagonalization of the three-orbital Hubbard model, we observe the effect of strong correlations manifesting in a dynamical spectral weight transfer from the upper Hubbard band to the ZRS band. The quantitative agreement between theory and experiment highlights an additional spectral weight reshuffling due to core-hole interaction. Our results confirm the important correlated nature of the cuprates and elucidate the changing orbital character of the low-energy quasi-particles, but also demonstrate the continued relevance of the ZRS even in the overdoped region.Comment: Original: 5 pages, 4 figures. Replaced: 6 pages and 4 figures, with updated title and conten

The variation of floods in the middle reaches of the Yangtze River and its teleconnection with El Niño events

International audienceMiddle reaches of the Yangtze River are the worst flooded segments along the Yangtze River. It is important to understand and study the variations of frequency and magnitude of historical floods in this area and how were they related to or affected by EI Niño in a long historical period. We applied the statistics and time series to study and analyze historical floods (1470-2000) and EI Niño events (1525-1995). The results show that the more floods occurred in the latest 200 years. The power-spectral analysis suggests the main cycle of flood variation is longer than that of EI Niño events. El Nino shows the fluctuations of about 2-year and 3~4 year period while the flood variation is not so significant but can also be identified in the period of 2, 8 and 40 years (it exceeds the level of confidence 0.03). Time series analyses of the fluctuation of flood and El Nino indicate that there is a significant correlation between the two at both high and moderate frequency sections. The result shows that the response of the floods along the middle reaches of the Yangtze River to the effects of El Nino events is not only delayed one or more than one year as suggested by many Chinese scientists, but it also can be somewhat longer delayed up to about 8 years. The result also indicates that the shorter the interval of EI Niño events, the sooner the flood events follows. In other words, flood could be delayed with longer time if the interval time of EI Niño events is longer

Probing the inter-layer exciton physics in a MoS2_2/MoSe2_2/MoS2_2 van der Waals heterostructure

Stacking atomic monolayers of semiconducting transition metal dichalcogenides (TMDs) has emerged as an effective way to engineer their properties. In principle, the staggered band alignment of TMD heterostructures should result in the formation of inter-layer excitons with long lifetimes and robust valley polarization. However, these features have been observed simultaneously only in MoSe$_2$/WSe$_2$ heterostructures. Here we report on the observation of long lived inter-layer exciton emission in a MoS$_2$/MoSe$_2$/MoS$_2$ trilayer van der Waals heterostructure. The inter-layer nature of the observed transition is confirmed by photoluminescence spectroscopy, as well as by analyzing the temporal, excitation power and temperature dependence of the inter-layer emission peak. The observed complex photoluminescence dynamics suggests the presence of quasi-degenerate momentum-direct and momentum-indirect bandgaps. We show that circularly polarized optical pumping results in long lived valley polarization of inter-layer exciton. Intriguingly, the inter-layer exciton photoluminescence has helicity opposite to the excitation. Our results show that through a careful choice of the TMDs forming the van der Waals heterostructure it is possible to control the circular polarization of the inter-layer exciton emission.Comment: 19 pages, 3 figures. Just accepted for publication in Nano Letters (http://pubs.acs.org/doi/10.1021/acs.nanolett.7b03184

A Network Model of Goals Boosts Convergent Creativity Performance

To increase employee creativity is critical for organizational success, and yet we still know very little about what organizational contexts promote creative performance. Our research proposes that goal regulation in the workplace may have consequences for creativity. While there is an increasing trend for organizations and workers to visualize the structure of their goals (e.g., management hierarchy, concept-map, flowchart), prior research suggests the visualization approaches differ as one of the three types: hierarchical, network, and sequential models. Because a network model (vs. hierarchical and sequential models) highlights multiple connections between goals and reveals unobvious connections between them, we hypothesized that the use of a network goal model might increase people’s ability to integrate seemingly unrelated ideas, even on subsequent unrelated tasks, leading to higher (convergent) creative performance. To test the hypothesis, we conducted an experiment in 2017 manipulating participants’ goal models (hierarchical, network, sequential; N = 191, median age = 19) and measured their creativity. Results suggest that those in the network model condition performed better in the kind of creativity task that requires meaningful integration of unrelated ideas (i.e., convergent creativity); in contrast, there was no difference between goal model conditions on divergent creative performance. These findings thus illuminate how goal models may influence creativity, providing new insights into situational inductions that can boost creative performance. Theoretical and practical implications, limitations, and future directions of the work are discussed