Electronic superlattice revealed by resonant scattering from random impurities in Sr3Ru2O7

Resonant elastic x-ray scattering (REXS) is an exquisite element-sensitive tool for the study of subtle charge, orbital, and spin superlattice orders driven by the valence electrons, which therefore escape detection in conventional x-ray diffraction (XRD). Although the power of REXS has been demonstrated by numerous studies of complex oxides performed in the soft x-ray regime, the cross section and photon wavelength of the material-specific elemental absorption edges ultimately set the limit to the smallest superlattice amplitude and periodicity one can probe. Here we show -- with simulations and REXS on Mn-substituted Sr$_3$Ru$_2$O$_7$ -- that these limitations can be overcome by performing resonant scattering experiments at the absorption edge of a suitably-chosen, dilute impurity. This establishes that -- in analogy with impurity-based methods used in electron-spin-resonance, nuclear-magnetic resonance, and M\"ossbauer spectroscopy -- randomly distributed impurities can serve as a non-invasive, but now momentum-dependent probe, greatly extending the applicability of resonant x-ray scattering techniques

Crystal-field level inversion in lightly Mn-doped Sr3Ru2O7

Sr3(Ru1-xMnx)2O7, in which 4d-Ru is substituted by the more localized 3d-Mn, is studied by x-ray dichroism and spin-resolved density functional theory. We find that Mn impurities do not exhibit the same 4+ valence of Ru, but act as 3+ acceptors; the extra eg electron occupies the in-plane 3dx2-y2 orbital instead of the expected out-of-plane 3d3z2-r2. We propose that the 3d-4d interplay, via the ligand oxygen orbitals, is responsible for this crystal-field level inversion and the material's transition to an antiferromagnetic, possibly orbitally-ordered, low-temperature state.Comment: A high-resolution version can be found at http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/MnSr3Ru2O7_XAS.pd

WARNING: Physics Envy May Be Hazardous To Your Wealth!

The quantitative aspirations of economists and financial analysts have for many years been based on the belief that it should be possible to build models of economic systems - and financial markets in particular - that are as predictive as those in physics. While this perspective has led to a number of important breakthroughs in economics, "physics envy" has also created a false sense of mathematical precision in some cases. We speculate on the origins of physics envy, and then describe an alternate perspective of economic behavior based on a new taxonomy of uncertainty. We illustrate the relevance of this taxonomy with two concrete examples: the classical harmonic oscillator with some new twists that make physics look more like economics, and a quantitative equity market-neutral strategy. We conclude by offering a new interpretation of tail events, proposing an "uncertainty checklist" with which our taxonomy can be implemented, and considering the role that quants played in the current financial crisis.Comment: v3 adds 2 reference

Development of high temperature superconducting current feeders for a large-scale superconducting experimental fusion system

The National Institute for Fusion Science (NIFS), in collaboration with universities and laboratories in Japan, the Forschungszentrum Karlsruhe (FZK) and the Max-Planck Institut fur Plasma Physik (IPP) in Germany, is planning to develop high temperature superconducting (HTS) current feeders for large-scale superconducting coils. Two programs are being progressed: one is a current feedthrough for superfluid helium (He II) cooled superconducting coils; the other is current leads for experimental fusion system. The paper describes the present status of the two programs, including joint experiments of a 20 kA Bi-2223 current lead developed by FZK and development of a prototype YBCO bulk current feedthrough for He II cooled superconducting coils. In addition, the test results of Bi-2212 tubes fabricated by diffusion process, applicable to HTS current leads, are described Bi_2Sr_2 CaCu_2O_

Application of high temperature superconductor in National Institute for Fusion Science

In the National Institute for Fusion Science (NIFS), the following three research items are being advanced as application of high temperature superconductor (HTS) to an experimental fusion plasma system, through collaboration with universities and laboratories. The first is an application of HTS in the large current feedthrough to a superconducting coil cooled with superfluid helium in order to reconcile low heat load and stable large current transport capability. A 20 kA current feedthrough from 4.4 K to 1.8 K has been being developed using YBCO bulk superconductors manufactured by the QMG process. The second is the development of a 30 kA HTS current lead. The Bi2212 bulk material fabricated by the diffusion process is considered as a candidate material for HTS current leads. The third is the development of the superconducting magnetic-levitation coil for Mini-RT wound with Bi2223 tape conductor. A magnetic-levitation coil operated in persistent-current mode has to levitate for 8 hours without a feed of refrigerant. Present status of these HTS application researches in NIFS is reported

What controls the isotopic composition of Greenland surface snow?

International audienceWater stable isotopes in Greenland ice core data provide key paleoclimatic information, and have been compared with precipitation isotopic composition simulated by isotopically enabled atmospheric models. However, post-depositional processes linked with snow metamorphism remain poorly documented. For this purpose, monitoring of the isotopic composition (d18O, dD) of near-surface water vapor, precipitation and samples of the top (0.5 cm) snow surface has been conducted during two summers (2011-2012) at NEEM, NW Greenland. The samples also include a subset of 17O-excess measurements over 4 days, and the measurements span the 2012 Greenland heat wave. Our observations are consistent with calculations assuming isotopic equilibrium between surface snow and water vapor. We observe a strong correlation between near-surface vapor d18O and air temperature (0.85 ± 0.11‰ °C-1 (R = 0.76) for 2012). The correlation with air temperature is not observed in precipitation data or surface snow data. Deuterium excess (d-excess) is strongly anti-correlated with d18O with a stronger slope for vapor than for precipitation and snow surface data. During nine 1-5-day periods between precipitation events, our data demonstrate parallel changes of d18O and d-excess in surface snow and near-surface vapor. The changes in d18O of the vapor are similar or larger than those of the snow d18O. It is estimated using the CROCUS snow model that 6 to 20% of the surface snow mass is exchanged with the atmosphere. In our data, the sign of surface snow isotopic changes is not related to the sign or magnitude of sublimation or deposition. Comparisons with atmospheric models show that day-to-day variations in near-surface vapor isotopic composition are driven by synoptic variations and changes in air mass trajectories and distillation histories. We suggest that, in between precipitation events, changes in the surface snow isotopic composition are driven by these changes in near-surface vapor isotopic composition. This is consistent with an estimated 60% mass turnover of surface snow per day driven by snow recrystallization processes under NEEM summer surface snow temperature gradients. Our findings have implications for ice core data interpretation and model-data comparisons, and call for further process studies. © Author(s) 2014

Performance of the LHD cryogenic system during cooling and excitation tests

Performance of the LHD cryogenic system in the first year\u27s operation was described making importance on the recovery process after the normal transition of the helical coils. During the excitation tests of the LHD superconducting coils up to 2.75 T, the normal zone propagation was observed in the helical coil and the emergency shut-off of the coil power supplies was carried out. 2,700 l of liquid helium evaporated from the helical coils. The coils and the helium refrigerator were separated automatically and the helium refrigerator could keep its steady state operation. After the pressure and flow rate of the recovery gas from the helical coils were settled down to the normal state, the coils were connected to the helium refrigerator and the cooling was restarted. The system could return to the steady state in which coil excitation is enabling, by only three and a half hour