Yiming Qiu

DAVE: A Comprehensive Software Suite for the Reduction, Visualization, and Analysis of Low Energy Neutron Spectroscopic Data

National user facilities such as the NIST Center for Neutron Research (NCNR) require a significant base of software to treat the data produced by their specialized measurement instruments. There is no universally accepted and used data treatment package for the reduction, visualization, and analysis of inelastic neutron scattering data. However, we believe that the software development approach adopted at the NCNR has some key characteristics that have resulted in a successful software package called DAVE (the Data Analysis and Visualization Environment). It is developed using a high level scientific programming language, and it has been widely adopted in the United States and abroad. In this paper we describe the development approach, elements of the DAVE software suite, its usage and impact, and future directions and opportunities for development.

Spin Gap and Resonance at the Nesting Wave Vector in Superconducting FeSe0:4Te0:6

Neutron scattering is used to probe magnetic excitations in FeSe_{0.4}Te_{0.6} (T_{c} = 14 K). Low energy spin fluctuations are found with a characteristic wave vector (1/21/2L) that corresponds to Fermi surface nesting and differs from Q_{m} = (delta01/2) for magnetic ordering in Fe_{1+y}Te. A spin resonance with variant Plancks over 2piOmega_{0} = 6.51(4) meV approximately 5.3k_{B}T_{c} and variant Plancks over 2piGamma = 1.25(5) meV develops in the superconducting state from a normal state continuum. We show that the resonance is consistent with a bound state associated with s_{+/-} superconductivity and imperfect quasi-2D Fermi surface nesting.

From (π,0) magnetic order to superconductivity with (π,π) magnetic resonance in Fe1.02Te1−xSex

The iron chalcogenide Fe(1+y)(Te(1-x)Se(x)) is structurally the simplest of the Fe-based superconductors. Although the Fermi surface is similar to iron pnictides, the parent compound Fe(1+y)Te exhibits antiferromagnetic order with an in-plane magnetic wave vector (pi,0) (ref. 6). This contrasts the pnictide parent compounds where the magnetic order has an in-plane magnetic wave vector (pi,pi) that connects hole and electron parts of the Fermi surface. Despite these differences, both the pnictide and chalcogenide Fe superconductors exhibit a superconducting spin resonance around (pi,pi) (refs 9, 10, 11). A central question in this burgeoning field is therefore how (pi,pi) superconductivity can emerge from a (pi,0) magnetic instability. Here, we report that the magnetic soft mode evolving from the (pi,0)-type magnetic long-range order is associated with weak charge carrier localization. Bulk superconductivity occurs as magnetic correlations at (pi,0) are suppressed and the mode at (pi, pi) becomes dominant for x>0.29. Our results suggest a common magnetic origin for superconductivity in iron chalcogenide and pnictide superconductors.

Crystal Structure and Antiferromagnetic Order in NdFeAsO1 xFx (x ¼ 0:0 and 0.2) Superconducting Compounds from Neutron Diffraction Measurements

Y. Qiu, 2 Wei Bao, ∗ Q. Huang, T. Yildirim, J. M. Simmons, 2 M. A. Green, 2 J.W. Lynn, Y.C. Gasparovic, 2 J. Li, 2 T. Wu, G. Wu, and X.H. Chen NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA Los Alamos National Laboratory, Los Alamos, NM 87545, USA Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China

Soft phonon columns on the edge of the Brillouin zone in the relaxor PbMg1/3Nb2/3O3

which is similar to the onset temperature of the zone-center diffuse scattering, indicating a competition between ferroelectric and antiferroelectric distortions. We propose a model for the atomic displacements associated with these phonon modes that is based on a combination of structure factors and group theoretical analysis. This analysis suggests that the scattering is not from tilt modes rotational modes of oxygen octahedra, but from zone-boundary optic modes that are associated with the displacement of Pb 2+ and O 2� ions. Whereas similar columns of scattering have been reported in metallic and less commonly molecular systems, they are unusual in insulating materials, particularly in ferroelectrics; therefore, the physical origin of this inelastic feature in PMN is unknown. We speculate that the underlying disorder contributes to this unique anomaly.

Anisotropic and quasipropagating spin excitations in superconducting Ba(Fe0.926Co0.074)2As2

Inelastic neutron scattering from superconducting (SC) Ba(Fe

Liquidlike Correlations in Single-Crystalline Y2Mo2O7: An Unconventional Spin Glass

_{0.926}

Disordered Route to the Coulomb Quantum Spin Liquid: Random Transverse Fields on Spin Ice in Pr2Zr2O7

Co

Order by disorder spin wave gap in the XY pyrochlore magnet Er2Ti2O7.

_{0.074}

Effective spin- 12 scalar chiral order on kagome lattices in Nd3Sb3Mg2O14

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