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

Estimation of electrical parameters of large-scale superconducting coil system for fusion plasma experimental facility

The Large Helical Device (LHD) in the National Institute for Fusion Science (NIFS) has six sets of large scale superconducting coils and six dc power supplies to charge them. For the current controllers of these power supplies, high accuracy of current control, good response and robustness of system are required. In the design of the controller, it was pointed out that the correct inductance matrix of the coil system and some electrical parameters that describe metal structures such as a supporting shell are necessary. This paper introduces a method based on a frequency response of impedance to estimate these parameters. First, the measured inductances of the LHD superconducting coils, which are measured from coil terminals, are presented and discussed. Next, an estimation method for circuit parameters is described. Finally, an experimental result of coil excitation using these parameters is presented. The experimental result show that the coil current controller using the estimated model satisfies previous requirements and it is confirmed that this parameter estimation method is valid for the large scale coil system

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

Results of the first excitation of helical coils of the Large Helical Device

The helical coils of the Large Helical Device are large scale pool-cooled superconducting coils. A conductor made of NbTi-Cu compacted strands and a pure Al stabilizer was developed to attain high cryostability. The design current of the conductor is 13.0 kA at 4.4 K, which produces a toroidal magnetic field of 3 T at a major radius of 3.9 m. The first excitation test up to 6.5 kA was conducted successfully is the beginning of the first cooling period. The higher excitations were tried in the second cooling period. The first propagation of a normal zone was observed when reaching 11.2 kA, and it recovered within 5 s. In the next step, a wide propagation occurred at 11.4 kA, and the quench detection system worked. The coils were designed to satisfy `cold-end\u27 stability by using the recovery current measured in short samples, but a normal zone propagates at lower than the recovery current in the composite conductor stabilized by very low resistive meta