Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session B39: Focus Session: Iron Based Superconductors Synthesis and Doping |
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Sponsoring Units: DCMP DMP Chair: David Singh, Oak Ridge National Laboratory Room: F150 |
Monday, March 15, 2010 11:15AM - 11:51AM |
B39.00001: Synthesis and Doping of LaFeAsO, BaFe2As2, and FeTe Compounds Invited Speaker: This talk is an overview of the various synthesis techniques used in making the high-temperature Fe-superconductors based on LaFeAsO, BaFe2As2, and FeTe, and the chemical-doping dependent phase diagrams established for these three families. Some of the basic physical properties will be discussed, along with the calculated electronic structures and neutron scattering results on the parents and their doped phases. [Preview Abstract] |
Monday, March 15, 2010 11:51AM - 12:03PM |
B39.00002: Flux growth at ambient pressure of millimeter-sized single crystals of LaFeAsO, LaFeAsO$_{1-x}$F$_{x}$, and LaFe$_{1-x}$Co$_{x}$AsO Jiaqiang Yan, S. Nandi, J.L. Zarestky, W. Tian, A. Kreyssig, B. Jensen, A. Kracher, K.W. Dennis, R.J. McQueeney, A.I. Goldman, R.W. McCallum, T.A. Lograsso Millimeter-sized single crystals of LaFeAsO, LaFeAsO$_{1-x}$F$_{x}$, and LaFe$_{1-x}$Co$_{x}$AsO were grown in NaAs flux at ambient pressure. The as-grown crystals have typical dimensions of 3 $\times$ 4 $\times$ 0.05-0.3 mm$^{3}$ with the crystallographic $c$-axis perpendicular to the plane of the plate-like single crystals. Various characterizations confirmed the high quality of our LaFeAsO crystals. Co and F were introduced into the lattice leading to superconducting LaFe$_{1-x}$Co$_{x}$AsO and LaFeAsO$_{1-x}$F$_{x}$ single crystals, respectively. The distribution and control of Co and F dopants will be discussed. - Ames Laboratory is operated for the US Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358. [Preview Abstract] |
Monday, March 15, 2010 12:03PM - 12:15PM |
B39.00003: Single crystal growth and superconductivity of Fe-Te-Se materials G.D. Gu, Jinsheng Wen, Zhijun Xu, M. Enoki, Z.W. Lin, Qiang Li, J.M. Tranquada A number of Fe-base superconducting materials with critical superconducting temperature up to 56K have been discovered in 2008. Fe-Te-Se is ``11'' system superconductor which has the simplest crystal structure. We have grown a number of the FeTe$_{1-x}$Se$_{x}$ single crystals (x = 0$\sim $0.7) by using a Bridgman growth technique. The effects of the growth condition and the composition of a feed rod on the single crystal growth of Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ have been studied. The single crystals of the PbO-type tetragonal structure Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ with high extra Fe (\textit{ie} y$>$0) are not superconducting. When Se substitutes for Te in FeTe$_{1-x}$Se$_{x}$ single crystals, the superconducting transition temperature increases with increasing Se content. The maximum Tc of FeTe$_{0.5}$Se$_{0.5 }$is 15K. [Preview Abstract] |
Monday, March 15, 2010 12:15PM - 12:27PM |
B39.00004: ABSTRACT WITHDRAWN |
Monday, March 15, 2010 12:27PM - 12:39PM |
B39.00005: Density Functional Study of the Electronic Structure and Magnetism of LaFeAsO alloyed with Zn Lijun Zhang, David Singh The effect of substitution of Fe by the non-magnetic 3$d$ element, Zn in LaFeAsO is investigated by first-principles supercell calculations. As expected, Zn occurs in a $d^{10}$ configuration, with the $d$ states fully occupied at higher binding energy in LaFe$_{1-x}$Zn$_{x}$AsO, similar to the pure Zn compound LaZnAsO. This is highly disruptive to the electronic structure of LaFeAsO near the Fermi energy, which is dominated by the partially filled Fe $d$ shell. Further, this favors localization, the formation of moments on the Fe atoms in proximity to the Zn, and magnetic states that compete with the spin density wave. These results are discussed in relation to experimental observations for Zn substituted LaFeAsO. [Preview Abstract] |
Monday, March 15, 2010 12:39PM - 12:51PM |
B39.00006: Physical properties FeSe$_{1-x}$Te$_{x }$ single crystals Tesfay Gebre, Luis Balicas, Yan Xin, Jeffrey Whalen, Theo Siegrist Single crystals of FeSe$_{1-x}$Te$_{x}$ were synthesized by both optical floating zone and self-flux techniques. Crystals were characterized via EDX, x-ray scattering, magnetization and galvanometric measurements. We have found that these compounds are particularly resilient to the application of high magnetic fields. Upper critical fields as estimated through the WHH formalism indicate that these materials strongly surpass the weak coupling Pauli limiting field indicating that the shape of their phase diagram under field is essentially controlled by the Pauli effect. The evolution of the phase diagram as a function of doping and magnetic field will be presented. [Preview Abstract] |
Monday, March 15, 2010 12:51PM - 1:03PM |
B39.00007: Phase diagram of 11 type iron-based superconductors from FeSe to FeTe Yoshihiko Takano, Yoshikazu Mizuguchi FeSe has the simplest crystal structure in the iron-based superconductors. The structural phase transition from tetragonal to orthorhombic took place around 70K without magnetic ordering. Surprisingly, the superconducting transition temperature Tc raised from 13K to 37K under the pressure of around 4-6GPa. We also observed the strong relation between Tc and 1/T1T in NMR under pressure, which suggesting that the superconductivity and spin fluctuation is closely related. STM measurements have performed at low temperature. The detailed information will be presented. On the other hand, pure FeTe shows structural and magnetic transition around 70K, and superconductivity was not observed. Recently we have succeeded to realize superconductivity in FeTe by S doping around 10K. Phase diagram of 11 type from FeSe to FeTe were summarized and discussed about the relation of superconductivity and magnetism. [Preview Abstract] |
Monday, March 15, 2010 1:03PM - 1:15PM |
B39.00008: Chemical control of the superconductivity in NaFeAs and LiFeAs derivatives Simon Clarke, Dinah Parker, Michael Pitcher, Stephen Blundell, Tom Lancaster, Isabel Franke, Jack Wright, Peter Baker, Francis Pratt The correlation of composition with structure and physical properties will be described for the ``111'' series of alkali metal iron pnictides AFeAs (A = Li, Na). A combination of high resolution X-ray and neutron powder diffraction, muon-spin rotation spectroscopy and magnetometry measurements will be described which probe the competition between superconductivity and antiferromagnetism in stoichiometric NaFeAs and the cobalt- and nickel-doped derivatives. The behavior of these systems in which a superconducting dome is traversed as 0.1 electrons per Fe atom are added to the stoichiometric NaFeAs system will be discussed in relation to other classes of iron pnictide superconductors. The behavior of the doped NaFeAs system will be contrasted with the behavior of the doped LiFeAs system, for which the stoichiometric composition shows the optimal superconducting properties. The extremely high sensitivity of the LiFeAs system to composition and Li/Fe disorder will also be described. The differences in behavior of the NaFeAs and LiFeAs systems and the differing responses of the electronic properties of the two systems to applied hydrostatic pressure will be related to the structural parameters. [Preview Abstract] |
Monday, March 15, 2010 1:15PM - 1:27PM |
B39.00009: Evolution of superconductivity in SrFe$_2$As$_2$ with Ni and Pt substitution S.R. Saha, T. Drye, K. Kirshenbaum, N.P. Butch, X. Zhang, R. Greene, J. Paglione The superconducting state in the iron pnictide compounds with tetragonal ThCr$_2$Si$_2$ crystal structure has attracted much interest. Transition metal substitution is known to suppress the antiferromagnetic phase of the parent compounds, yielding superconductivity with maximum $T_c$ values approaching $\sim$20-25~K when Co, Ni, Ru, Rh, Pd, or Ir are used to replace Fe. However, this trend is known to be broken in the case of SrFe$_{2-x}$Ni$_x$As$_2$ and SrFe$_{2-x}$Pd$_x$As$_2$, which both exhibit reduced maximum $T_c$ values of order 10~K. We will present the effects of Ni and Pt substitution in single crystalline SrFe$_2$As$_2$ as measured by resistivity, magnetic susceptibility and specific heat, and discuss how our results relate to the isoelectronic case of Pd substitution as well as other neighboring transition metal substitution series. [Preview Abstract] |
Monday, March 15, 2010 1:27PM - 1:39PM |
B39.00010: Ternary iron pnictides $AFe_2As_2$ (A = alkali metal) and LiFeAs: A systematic study of magnetic properties and transport measurements Melissa Gooch, Bing Lv, Kalyan Sasmal, Bernd Lorenz, Joshua Tapp, Zhongjia Tang, Arnold Guloy, Ching-Wu Chu We have observed superconductivity for the alkali metal $AFe_2As_2$, where A = Cs, Rb, and K, at temperatures below 4 K. In addition to the above mentioned ternary compounds we also were able to synthesize and measure the metastable superconducting $NaFe_2As_2$, which has a considerably higher superconducting transition at 25 K. The ternary iron pnictides $AFe_2As_2$ are all considered strongly hole over-doped superconductors. LiFeAs is superconducting with a $T_c$ of 18 K. Thermoelectric power measurements indicate that a majority of carriers are electron like, which supports our conjecture that LiFeAs is a stoichiometric superconductor. The effects of high pressure on the $T_c$ will also be discussed. [Preview Abstract] |
Monday, March 15, 2010 1:39PM - 1:51PM |
B39.00011: Superconductivity and Unusual Magnetism in the Solid Solution NdFe$_{1-x}$Co$_{x}$AsO Michael McGuire, Delphine Gout, Vasile Garlea, Athena Sefat, Brian Sales, David Mandrus NdFeAsO is a low carrier concentration semimetal which undergoes a spin density wave transition, and is a parent phase of iron pnictide superconductors. Doping with fluorine is known to produce superconductivity with Tc up to 52 K. Through a study of the solid solution NdFe$_{1-x}$Co$_{x}$AsO, we demonstrate that replacement of iron with cobalt also induces superconductivity, as has been reported for several other iron pnictide systems. Of particular interest in this system is the end-member NdCoAsO, which shows unusual magnetic behavior. This material undergoes three magnetic phase transitions at low temperatures. We report a detailed study of NdCoAsO including results from transport, magnetization, and heat capacity measurements, as well as neutron diffraction. [Preview Abstract] |
Monday, March 15, 2010 1:51PM - 2:03PM |
B39.00012: Doping-dependent inter-plane transport in electron doped Ba(Fe,$TM$)$_2$As$_2$ ($TM$=Co, Ni, Rh, Pd) M. A. Tanatar, N. Ni, A. N. Thaler, S. L. Bud'ko, P. C. Canfield, Ruslan Prozorov We report comprehensive characterization of the inter-plane resistivity in Ba(Fe,$TM$)$_2$As$_2$ as a function of transition metal doping, $TM$=Co, Ni, Pd, Rh. For all dopants we find different $T$-dependence of in-plane and inter-plane transport and moderate resistivity anisotropy at room temperature. The temperature-dependent inter-plane transport correlates well with NMR Knight shift and relaxation time [1], revealing effect of spin gap on electrical charge transport in iron-arsenic compounds. Doping phase diagram of the behavior is determined. [1] F. Ning, {\ it et al.} J. Phys. Soc. Jpn {\bf 78}, 013711 (2009). [Preview Abstract] |
Monday, March 15, 2010 2:03PM - 2:15PM |
B39.00013: Evolution of Crystal Structure and Magnetism in Single-Crystal (Ba,Sr,Ca)Fe$_2$As$_2$ Solid Solutions Johnpierre Paglione, K. Kirshenbaum, S.R. Saha, N.P. Butch, P.Y. Zavalij, B.G. Ueland, J.W. Lynn Superconductivity in the FeAs-based materials has motivated extensive studies of structural, magnetic and electronic properties of these systems. A common element of the 122 FeAs- based intermetallic series is the occurrence of a simultaneous structural and antiferromagnetic phase transition, which occurs at temperatures ranging between 130 K and 200 K in the Ba, Sr, and Ca-based parent compounds. We present a systematic study of the evolution of the magnetic and structural properties of solid solutions of these parent compounds obtained through electrical transport, magnetic susceptibility, x-ray and neutron scattering measurements of single-crystal samples, discussing the relation between magnetic order and structural aspects through the solid solution series. [Preview Abstract] |
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