We explore a new type of domain wall structure in ultrathin films with perpendicular anisotropy, that is influenced by the Dzyaloshinskii-Moriya interaction due to the adjacent layers. This study is performed by numerical and analytical micromagnetics. We show that these walls can behave like Neel walls with very high stability, moving in stationary conditions at large velocities under large fields. We discuss the relevance of such walls, that we propose to call Dzyaloshinskii domain walls, for current-driven domain wall motion under the spin Hall effect. Copyright (c) EPLA, 2012
Revealing complicated behaviors from time series constitutes a fundamental problem of continuing interest and it has attracted a great deal of attention from a wide variety of fields on account of its significant importance. The past decade has witnessed a rapid development of complex network studies, which allow to characterize many types of systems in nature and technology that contain a large number of components interacting with each other in a complicated manner. Recently, the complex network theory has been incorporated into the analysis of time series and fruitful achievements have been obtained. Complex network analysis of time series opens up new venues to address interdisciplinary challenges in climate dynamics, multiphase flow, brain functions, ECG dynamics, economics and traffic systems. Copyright (C) EPLA, 2016
(Tl,K)FexSe2 single crystals were first successfully synthesized with the Bridgeman method. The physical properties are characterized by electrical resistivity, magnetic susceptibility and Hall coefficient. We found that the (Tl,K)FexSe2 (1.30 <= x <= 1.65) compounds show an antiferromagetic (AFM) insulator behavior, which may be associated with the Fe-vacancy ordering in the crystals. While in the 1.70 <= x < 1.78 crystals, superconductivity (SC) coexists with an insulating phase. As Fe content further increases, the bulk SC with T-c = 31K (and a T-c(onset) as high as 40 K) appears in the 1.78 <= x <= 1.88 crystals. Our discovery represents the first Fe-based high-temperature superconductivity (HTSC) at the verge of an AFM insulator. Copyright (C) EPLA, 2011
We have performed a high-resolution angle- resolved photoelectron spectroscopy study on the newly discovered superconductor Ba0.6K0.4Fe2As2 (T-c = 37 K). We have observed two superconducting gaps with different values: a large gap (Delta similar to 12 meV) on the two small hole-like and electron-like Fermi surface (FS) sheets, and a small gap (similar to 6meV) on the large hole-like FS. Both gaps, closing simultaneously at the bulk transition temperature (T-c), are nodeless and nearly isotropic around their respective FS sheets. The isotropic pairing interactions are strongly orbital dependent, as the ratio 2 Delta/k(B)T(c) switches from weak to strong coupling on different bands. The same and surprisingly large superconducting gap due to strong pairing on the two small FSs, which are connected by the (pi, 0) spin-density-wave vector in the parent compound, strongly suggests that the pairing mechanism originates from the inter-band interactions between these two nested FS sheets. Copyright (c) EPLA, 2008.
We study the evolution of public cooperation on two interdependent networks that are connected by means of a utility function, which determines to what extent payoffs in one network influence the success of players in the other network. We find that the stronger the bias in the utility function, the higher the level of public cooperation. Yet the benefits of enhanced public cooperation on the two networks are just as biased as the utility functions themselves. While cooperation may thrive on one network, the other may still be plagued by defectors. Nevertheless, the aggregate level of cooperation on both networks is higher than the one attainable on an isolated network. This positive effect of biased utility functions is due to the suppressed feedback of individual success, which leads to a spontaneous separation of characteristic time scales of the evolutionary process on the two interdependent networks. As a result, cooperation is promoted because the aggressive invasion of defectors is more sensitive to the slowing-down than the build-up of collective efforts in sizable groups. Copyright (C) EPLA, 2012
Active Brownian particles (ABPs, such as self-phoretic colloids) swim at fixed speed v along a body-axis u that rotates by slow angular diffusion. Run-and-tumble particles (RTPs, such as motile bacteria) swim with constant u until a random tumble event suddenly decorrelates the orientation. We show that when the motility parameters depend on density rho but not on u, the coarse-grained fluctuating hydrodynamics of interacting ABPs and RTPs can be mapped onto each other and are thus strictly equivalent. In both cases, a steeply enough decreasing v(rho) causes phase separation in dimensions d=2, 3, even when no attractive forces act between the particles. This points to a generic role for motility-induced phase separation in active matter. However, we show that the ABP/RTP equivalence does not automatically extend to the more general case of u-dependent motilities. Copyright (C) EPLA, 2013
Here we report a new quaternary iron-arsenide superconductor Nd[O1-xFx]FeAs, with the onset resistivity transition at 51.9K and Meissner transition at 51 K. This compound has the same crystal structure as LaOFeAs, and becomes the second superconductor after Pr[O1-xFx]FeAs that superconducts above 50K. Copyright (c) EPLA, 2008.
TOTEM has measured the differential cross-section for elastic proton-proton scattering at the LHC energy of root s = 7 TeV analysing data from a short run with dedicated large-beta* optics. A single exponential fit with a slope B = (20.1 +/- 0.2(stat) +/- 0.3(syst)) GeV-2 describes the range of the four-momentum transfer squared vertical bar t vertical bar from 0.02 to 0.33 GeV2. After the extrapolation to vertical bar t vertical bar = 0, a total elastic scattering cross-section of (24.8 +/- 0.2(stat) +/- 1.2(syst)) mb was obtained. Applying the optical theorem and using the luminosity measurement from CMS, a total proton-proton cross-section of (98.3 +/- 0.2(stat) +/- 2.8(syst)) mb was deduced which is in good agreement with the expectation from the overall fit of previously measured data over a large range of center-of-mass energies. From the total and elastic pp cross-section measurements, an inelastic pp cross-section of (73.5 +/- 0.6(stat) (+1.8)(-1.3) (syst)) mb was inferred.
The interplay between different ordered phases, such as superconducting, charge or spin ordered phases, is of central interest in condensed-matter physics. The very recent discovery of superconductivity with a remarkable T-c = 26K in Fe-based oxypnictide La(O1-xFx) FeAs (see Kamihara Y. et al., J. Am. Chem. Soc., 130 (2008) 3296) is a surprise to the scientific community and has generated tremendous interest. The pure LaOFeAs itself is not superconducting but shows an anomaly near 150K in both resistivity and dc magnetic susceptibility. Here we provide combined experimental and theoretical evidences showing that a spin-density-wave (SDW) state develops at low temperature, in association with electron Nematic order. The electron-doping by F suppresses the SDW instability and induces the superconductivity. Therefore, the La(O1-xFx) FeAs offers an exciting new system showing competing orders in layered compounds. Copyright (C) EPLA, 2008.
The promise of punishment and reward in promoting public cooperation is debatable. While punishment is traditionally considered more successful than reward, the fact that the cost of punishment frequently fails to offset gains from enhanced cooperation has lead some to reconsider reward as the main catalyst behind collaborative efforts. Here we elaborate on the "stick vs. carrot" dilemma by studying the evolution of cooperation in the spatial public goods game, where besides the traditional cooperators and defectors, rewarding cooperators supplement the array of possible strategies. The latter are willing to reward cooperative actions at a personal cost, thus effectively downgrading pure cooperators to second-order free-riders due to their unwillingness to bear these additional costs. Consequently, we find that defection remains viable, especially if the rewarding is costly. Rewards, however, can promote cooperation, especially if the synergetic effects of cooperation are low. Surprisingly, moderate rewards may promote cooperation better than high rewards, which is due to the spontaneous emergence of cyclic dominance between the three strategies. Copyright (C) EPLA, 2010
Here we report a new class of superconductors prepared by high-pressure synthesis in the quaternary family ReFeAsO1-delta (Re = Sm, Nd, Pr, Ce, La) without fluorine doping. The onset superconducting critical temperature (T-c) in these compounds increases with the reduction of the Re atom size, and the highest T-c obtained so far is 55K in SmFeAsO1-delta. For the NdFeAsO1-delta compound with different oxygen concentration a dome-shaped phase diagram was found. Copyright (c) EPLA, 2008.
We report a new strategy to induce superconductivity in iron-based oxyarsenide. Instead of F- substitution for O2-, we employed Th4+ doping in GdFeAsO with the consideration of "lattice match" between Gd2O2 layers and Fe2As2 ones. As a result, superconductivity with T-c(onset) as high as 56 K was realized in a Gd0.8Th0.2FeAsO polycrystalline sample. This T-c value is among the highest ever discovered in the iron-based oxypnictides. Copyright (C) EPLA, 2008
Collective behavior among coupled dynamical units can emerge in various forms as a result of different coupling topologies as well as different types of coupling functions. Chimera states have recently received ample attention as a fascinating manifestation of collective behavior, in particular describing a symmetry breaking spatiotemporal pattern where synchronized and desynchronized states coexist in a network of coupled oscillators. In this perspective, we review the emergence of different chimera states, focusing on the effects of different coupling topologies that describe the interaction network connecting the oscillators. We cover chimera states that emerge in local, nonlocal and global coupling topologies, as well as in modular, temporal and multilayer networks. We also provide an outline of challenges and directions for future research. Copyright (C) EPLA, 2017
We describe the slippery behaviour of textured solids filled with oil, on which other liquids are found to slip and be removed easily. We describe the criteria for achieving this slippery behaviour, and illustrate the concept by two examples, namely the lotus effect (removal of dust by mobile drops) and the coffee stain effect. Copyright (C) EPLA, 2011
We have carried out a systematic study of the PbO-type compound FeSe1-xTex (x = 0-1), where the Te substitution effect on superconductivity is investigated. It is found that the superconducting transition temperature reaches a maximum of T-c = 15.2 K at about 50% Te substitution. The pressure-enhanced Tc of FeSe0.5Te0.5 is more than 10 times larger than that of FeSe. Interestingly, FeTe is no longer superconducting. A low-temperature structural distortion changes FeTe from triclinic symmetry to orthorhombic symmetry. We believe that this structural change breaks the magnetic symmetry and suppresses superconductivity in FeTe. Copyright (C) EPLA, 2008
Noisy signals in many real-world systems display long-range autocorrelations and long-range cross-correlations. Due to periodic trends, these correlations are difficult to quantify. We demonstrate that one can accurately quantify power-law cross-correlations between different simultaneously recorded time series in the presence of highly non-stationary sinusoidal and polynomial overlying trends by using the new technique of detrended cross-correlation analysis with varying order l of the polynomial. To demonstrate the utility of this new method-which we call DCCA-l(n), where n denotes the scale-we apply it to meteorological data. Copyright (C) EPLA, 2011
We consider percolation on interdependent locally treelike networks, recently introduced by BULDYREV S. V. et al., Nature, 464 (2010) 1025, and demonstrate that the problem can be simplified conceptually by deleting all references to cascades of failures. Such cascades do exist, but their explicit treatment just complicates the theory -which is a straightforward extension of the usual epidemic spreading theory on a single network. Our method has the added benefits that it is directly formulated in terms of an order parameter and its modular structure can be easily extended to other problems, e.g. to any number of interdependent networks, or to networks with dependency links. Copyright (C) EPLA, 2012
By partially substituting the tri-valence element La with di-valence element Sr in LaOFeAs, we introduced holes into the system. For the first time, we successfully synthesized the hole-doped new superconductors (La1-xSrx) OFeAs. The maximum superconducting transition temperature at about 25K was observed at a doping level of x=0.13. It is evidenced by Hall effect measurements that the conduction in this type of material is dominated by hole-like charge carriers, rather than electron-like ones. Together with the data of the electron-doped system La(O1-xFx) FeAs, a generic phase diagram is depicted and is revealed to be similar to that of the cuprate superconductors. Copyright (c) EPLA, 2008.