Annealing effects on superconductivity in SrFe2-xNixAs2

Superconductivity has been explored in single crystals of the Ni-doped FeAs-compound SrFe2-xNixAs2 grown by self-flux solution method. The antiferromagnetic order associated with the magnetostructural transition of the parent compound SrFe2As2 is gradually suppressed with increasing Ni concentration x and bulk-phase superconductivity with full diamagnetic screening is induced near the optimal doping of x = 0.15 with a maximum transition temperature Tc ~9.8 K. An investigation of high-temperature annealing on as-grown samples indicate that the heat treatment can enhance Tc as much as ~50 %

Effect of annealing on glassy dynamics and non-Fermi liquid behavior in UCu_4Pd

Longitudinal-field muon spin relaxation (LF-muSR) experiments have been performed in unannealed and annealed samples of the heavy-fermion compound UCu_4Pd to study the effect of disorder on non-Fermi liquid behavior in this material. The muon spin relaxation functions G(t,H) obey the time-field scaling relation G(t,H) = G(t/H^gamma) previously observed in this compound. The observed scaling exponent gamma = 0.3 pm 0.1, independent of annealing. Fits of the stretched-exponential relaxation function G(t) = exp[-(Lambda t)^K] to the data yielded stretching exponentials K < 1 for all samples. Annealed samples exhibited a reduction of the relaxation rate at low temperatures, indicating that annealing shifts fluctuation noise power to higher frequencies. There was no tendency of the inhomogeneous spread in rates to decrease with annealing, which modifies but does not eliminate the glassy spin dynamics reported previously in this compound. The correlation with residual resistivity previously observed for a number of NFL heavy-electron materials is also found in the present work.Comment: 4 pages, 3 figures, submitted to 10th International Conference on Muon Spin Rotation, Relaxation, and Resonance, Oxford, UK, August 200

Phase separation and superconductivity in Fe 1+xTe 0.5Se 0.5

Fe 1+xTe 0.5Se 0.5 is the archetypical iron-based superconductor. Here we show that the superconducting state is controlled by the stacking of its anti-PbO layers, such that homogeneous ordering hinders superconductivity and the highest volume fractions are observed in phase separated structures as evidenced by either a distribution of lattice parameters or microstrain. © 2011 The Royal Society of Chemistry

Chemical control of interstitial iron leading to superconductivity in Fe 1+xTe 0.7Se 0.3

Although it possesses the simple layered topology of the tetragonal anti-PO structure, the Fe(Te,Se) series has a complex structural and magnetic phase diagram that is dependent on composition and occupancy of a secondary interstitial Fe site. Here we show that superconductivity in Fe 1+xTe 0.7Se 0.3 is enhanced by topotactic deintercalation of the interstitial iron with iodine, demonstrating the competing roles of the two iron positions. We follow the evolution of the structure and magnetic properties as a function of interstitial iron. Powder neutron diffraction reveals a flattening of the Fe(Te,Se) 4 tetrahedron on Fe removal and an unusual temperature dependence of the lattice parameters that increases strongly below 150 K along with lattice strain. Inelastic neutron scattering shows gapless paramagnetic scattering evolves into a gapped excitation at 6 meV on removal of interstitial iron. This work highlights the robustness of the superconductivity across different Fe(Te,Se) compositions and geometries. © The Royal Society of Chemistry 2011

Phase separation and suppression of the structural and magnetic transitions in superconducting doped iron tellurides, Fe1+ xTe 1-ySy

Single crystal and powder samples of the series of iron chalcogenide superconductors with nominal composition, Fe1.15Te 1-ySy, are found to form for 0 â?¤ y â?¤ 0.15. They crystallize in the tetragonal anti-PbO structure, which is composed of layers of edge-shared Fe(Te, S)4 tetrahedra. For y = 0, Fe1+xTe (x â?? 0.12(1)) is nonsuperconducting and undergoes a tetragonal (P4/nmm) to monoclinic (P21/m) structural transition at â?¼65 K, associated with the onset of commensurate antiferromagnetic order at q = (0.5 0 0.5). We show that on sulfur substitution, Fe1+xTe1-ySy becomes orthorhombic (Pmmn) at low temperature for 0 â?¤ y â?¤ 0.015, where the greatly suppressed magnetic scattering is now incommensurate at q = (0.5-δ 0 0.5) and possesses short ranged magnetic correlations that are well fitted with a two-dimensional Warren peak shape. At much higher concentrations of S (y â?¤ 0.075), there is suppression of both the structural and magnetic transitions and a superconducting transition at 9 K is observed. Between these two composition regimes, there exists a region of phase separation (0.025 â?¤ y â?¤ 0.05), where the low temperature neutron diffraction data is best refined with a model containing both the tetragonal and orthorhombic phases. The increase in the amount of sulfur is found to be associated with a reduction in interstitial iron, x. Microprobe analysis of a single crystal of composition Fe1.123(5)Te0.948(4)S0.052(4) confirms the presence of compositional variation within the crystals, rationalizing the observed phase separation. © 2010 American Chemical Society

Global perspectives of the bulk electronic structure of URu2Si2 from angle-resolved photoemission

© 2022 The Author(s).Previous high-resolution angle-resolved photoemission (ARPES) studies of URu2Si2 have characterized the temperature-dependent behavior of narrow-band states close to the Fermi level (EF) at low photon energies near the zone center, with an emphasis on electronic reconstruction due to Brillouin zone folding. A substantial challenge to a proper description is that these states interact with other hole-band states that are generally absent from bulk-sensitive soft x-ray ARPES measurements. Here we provide a more global k-space context for the presence of such states and their relation to the bulk Fermi surface (FS) topology using synchrotron-based wide-angle and photon energy-dependent ARPES mapping of the electronic structure using photon energies intermediate between the low-energy regime and the high-energy soft x-ray regime. Small-spot spatial dependence, f-resonant photoemission, Si 2p core-levels, x-ray polarization, surface-dosing modification, and theoretical surface slab calculations are employed to assist identification of bulk versus surface state character of the EF-crossing bands and their relation to specific U- or Si-terminations of the cleaved surface. The bulk FS topology is critically compared to density functional theory (DFT) and to dynamical mean field theory calculations. In addition to clarifying some aspects of the previously measured high symmetry Γ, Z and X points, incommensurate 0.6a nested Fermi-edge states located along Z-N-Z are found to be distinctly different from the DFT FS prediction. The temperature evolution of these states above THO, combined with amore detailed theoretical investigation of this region, suggests a key role of the N-point in the hidden order transition.11Nscopu