201 research outputs found

    Resonant Inelastic X-ray Scattering on Spin-Orbit Coupled Insulating Iridates

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    We determine how the elementary excitations of iridium-oxide materials, which are dominated by a strong relativistic spin-orbit coupling, appear in Resonant Inelastic X-ray Scattering (RIXS). Whereas the RIXS spectral weight at the L2 x-ray edge vanishes, we find it to be strong at the L3-edge. Applying this to Sr2IrO4, we observe that RIXS, besides being sensitive to local doublet to quartet transitions, meticulously maps out the strongly dispersive delocalized excitations of the low-lying spin-orbit doublets.Comment: 4 pages, 3 figure

    Universal Short-time Behaviour of the Dynamic Fully Frustrated XY Model

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    With Monte Carlo methods we investigate the dynamic relaxation of the fully frustrated XY model in two dimensions below or at the Kosterlitz-Thouless phase transition temperature. Special attention is drawn to the sublattice structure of the dynamic evolution. Short-time scaling behaviour is found and universality is confirmed. The critical exponent θ\theta is measured for different temperature and with different algorithms.Comment: 18 pages, LaTeX, 8 ps-figure

    Dynamic SU(2) Lattice Gauge Theory at Finite Temperature

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    The dynamic relaxation process for the (2+1)--dimensional SU(2) lattice gauge theory at critical temperature is investigated with Monte Carlo methods. The critical initial increase of the Polyakov loop is observed. The dynamic exponents θ\theta and zz as well as the static critical exponent β/ν\beta/\nu are determined from the power law behaviour of the Polyakov loop, the auto-correlation and the second moment at the early stage of the time evolution. The results are well consistent and universal short-time scaling behaviour of the dynamic system is confirmed. The values of the exponents show that the dynamic SU(2) lattice gauge theory is in the same dynamic universality class as the dynamic Ising model.Comment: 10 pages with 2 figure

    Dynamic Approach to the Fully Frustrated XY Model

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    Using Monte Carlo simulations, we systematically investigate the non-equilibrium dynamics of the chiral degree of freedom in the two-dimensional fully frustrated XY model. The critical initial increase of the staggered chiral magnetization is observed. By means of the short-time dynamics approach, we estimate the second order phase transition temperature TcT_{c} and all the dynamic and static critical exponents θ\theta, z, β\beta and ν\nu.Comment: 5 pages with 6 figures include

    Dynamic Monte Carlo Study of the Two-Dimensional Quantum XY Model

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    We present a dynamic Monte Carlo study of the Kosterlitz-Thouless phase transition for the spin-1/2 quantum XY model in two dimensions. The short-time dynamic scaling behaviour is found and the dynamical exponent θ\theta, zz and the static exponent η\eta are determined at the transition temperature.Comment: 6 pages with 3 figure

    Imaging density disturbances in water with 41.3 attosecond time resolution

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    We show that the momentum flexibility of inelastic x-ray scattering may be exploited to invert its loss function, alowing real time imaging of density disturbances in a medium. We show the disturbance arising from a point source in liquid water, with a resolution of 41.3 attoseconds (4.13×10174.13 \times 10^{-17} sec) and 1.27 A˚\AA (1.27×1081.27 \times 10^{-8} cm). This result is used to determine the structure of the electron cloud around a photoexcited molecule in solution, as well as the wake generated in water by a 9 MeV gold ion. We draw an analogy with pump-probe techniques and suggest that energy-loss scattering may be applied more generally to the study of attosecond phenomena.Comment: 4 pages, 4 color figure

    Magnetic Excitations in La2CuO4 probed by Indirect Resonant Inelastic X-ray Scattering

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    Recent experiments on La2_2CuO4_4 suggest that indirect resonant inelastic X-ray scattering (RIXS) might provide a probe for transversal spin dynamics. We present in detail a systematic expansion of the relevant magnetic RIXS cross section by using the ultrashort core-hole lifetime (UCL) approximation. We compute the scattering intensity and its momentum dependence in leading order of the UCL expansion. The scattering is due to two-magnon processes and is calculated within a linear spin-wave expansion of the Heisenberg spin model for this compound, including longer range and cyclic spin interactions. We observe that the latter terms in the Hamiltonian enhance the first moment of the spectrum if they strengthen the antiferromagnetic ordering. The theoretical spectra agree very well with experimental data, including the observation that scattering intensity vanishes for the transferred momenta q=(0,0){\bf q} = (0,0) and q=(π,π){\bf q} = (\pi,\pi). We show that at finite temperature there is an additional single-magnon contribution to the scattering with a spectral weight proportional to T3T^3. We also compute the leading corrections to the UCL approximation and find them to be small, putting the UCL results on a solid basis. All this univocally points to the conclusion that the observed low temperature RIXS intensity in La2_2CuO4_4 is due to two-magnon scattering.Comment: 11 pages, 13 figures, Phys. Rev. B 77, 134428 (2008) (v4: corrected figs 7

    Dynamic Simulations of the Kosterlitz-Thouless Phase Transition

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    Based on the short-time dynamic scaling form, a novel dynamic approach is proposed to tackle numerically the Kosterlitz-Thouless phase transition. Taking the two-dimensional XY model as an example, the exponential divergence of the spatial correlation length, the transition temperature TKTT_{KT} and all critical exponents are computed. Compared with Monte Carlo simulations in equilibrium, we obtain data at temperatures nearer to TKTT_{KT}.Comment: to appear in Phys. Rev. E in Rapid Communicatio

    The evolution of social philopatry in female primates

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    The transition from solitary life to sociality is considered one of the major transitions in evolution. In primates, this transition is currently not well understood. Traditional verbal models appear insufficient to unravel the complex interplay of environmental and demographic factors involved in the evolution of primate sociality, and recent phylogenetic reconstructions have produced conflicting results. We therefore analyze a theoretical model for the evolution of female social philopatry that sheds new light on the question why most primates live in groups. In individual-based simulations, we study the evolution of dispersal strategies of both resident females and their offspring. The model reveals that social philopatry can evolve through kin selection, even if retention of offspring is costly in terms of within-group resource competition and provides no direct benefits. Our model supports the role of predator avoidance as a selective pressure for group-living in primates, but it also suggests that a second benefit of group-living, communal resource defense, might be required to trigger the evolution of sizable groups. Lastly, our model reveals that seemingly small differences in demographic parameters can have profound effects on primate social evolution

    Dynamic Approach to Weak First Order Phase Transitions

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    A short-time dynamic approach to weak first order phase transitions is proposed. Taking the 2-dimensional Potts models as examples, from short-time behaviour of non-equilibrium relaxational processes starting from high temperature and zero temperature states,x pseudo critical points K^{*} and K^{**} are determined. A clear difference of the values for K^{*} and K^{**} distinguishes a weak first order transition from a second order one. At the pseudo critical points, pseudo critical exponents can be estimated.Comment: 9 pages with 4 postscript figures include
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