Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session W26: Focus Session: Iron Based Superconductors -- Tuning Magnetism and Superconductivity |
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Sponsoring Units: DMP DCOMP Chair: David Mandrus, University of Tennessee and Oak Ridge National Laboratory Room: D162/164 |
Thursday, March 24, 2011 11:15AM - 11:27AM |
W26.00001: ABSTRACT WITHDRAWN |
Thursday, March 24, 2011 11:27AM - 11:39AM |
W26.00002: Superconductivity in (Sr,Ba)Fe2As2 single crystals by Pt substitution Tyler Drye, Shanta Saha, Kevin Kirshenbaum, Nicholas Butch, Johnpierre Paglione, Peter Zavalij Iron-based superconducting materials with the ThCr2Si2 tetragonal crystal structure appear to show a maximum superconducting transition temperature of Tc $\sim $ 20-25 K when transition metals (e.g., Co, Ni, Ru, Rh, Pd, or Ir) are substituted for Fe, effectively doping d-electrons and suppressing the antiferromagnetic order of the parent compounds. However, this trend is known to be broken in the case of SrFe2-xNixAs2 and SrFe2-xPdxAs2, which both have lower optimal Tc values near 10 K. We will present our recent work on Pt substitution in single crystalline BaFe2As2 and SrFe2As2, which induces a maximum Tc of 23 K and 17 K, respectively. The relation between Pt substitution in these systems and the related cases of isoelectronic Ni and Pd substitution will be discussed. [Preview Abstract] |
Thursday, March 24, 2011 11:39AM - 11:51AM |
W26.00003: Tetragonal lattice collapse in SrFe$_2$As$_2$ - a combined experimental and theoretical study Helge Rosner, Deepa Kasinathan, Miriam Schmitt, Alim Ormeci, Katrin Meier, Ulrich Schwarz, Michael Hanfland, Klaus Koepernik, Yuri Grin, Andreas Leithe-Jasper In a joint experimental and theoretical study we investigate the crystal structure of the Fe pnictide compounds SrFe$_2$As$_2$ under applied hydrostatic pressure. Applying high pressure X-ray diffractyion, for a critical pressure of about 10 GPa we observe a sudden collapse of the tetragonal $c$ axis, accompagnied by a small expansion of the basal plane. This results in a drastic reduction of the $c/a$ ratio and a significant decrease of the unit cell volume. This tetragonal collapse is well described by DFT band structure calculations and can be assigne d to the formation of an additional As-As bond along the tetragonal $c$ axis. [Preview Abstract] |
Thursday, March 24, 2011 11:51AM - 12:27PM |
W26.00004: Structural tuning of superconductivity and magnetism in intermetallic iron-pnictide materials Invited Speaker: The relationship between superconductivity, magnetism and crystallographic structure remains as one of the intriguing properties of the new family of iron-based superconducting materials. A well established requirement for high-temperature superconductivity in these systems is a substructure of iron ions tetrahedrally coordinated with either pnictogen or chalcogen anions stacked together to form a layered material, suggesting that both tetrahedral geometry and quasi-two-dimensionality are key ingredients. Through an investigation of solid solutions of (Ba,Sr,Ca)Fe$_2$As$_2$ series of parent compounds, we present a study of the importance of internal tetrahedral structure in stabilizing both magnetic and superconducting ground states in these materials, revealing an intimate relationship between the energy scale that dictates magnetic order and the internal structure of the FeAs$_4$ tetrahedra even far above the magnetic ordering temperature. In addition, interlayer coupling is investigated by exploiting the ``collapse'' of the tetragonal unit cell of CaFe$_2$As$_2$ under pressure, where interlayer pnictogen-pnictigen bonding changes dramatically. We investigate the effect of this collapse on superconductivity via chemical substitution, demonstrating an intriguing interplay of structure, magnetic and superconducting properties. [Preview Abstract] |
Thursday, March 24, 2011 12:27PM - 12:39PM |
W26.00005: Magnetic ordering in EuCo$_2$As$_2$ Balazs Sipos, Athena S. Sefat, Brian C. Sales We have synthesized and studied EuCo$_2$As$_2$ single crystals by resistivity, magnetoresistance, and susceptibility measurements. We found antiferromagnetic (AFM) ordering of the Eu spins at $T_N = 50$ K. Upon applying a magnetic field $H \| ab$ at $T = 2$ K this phase exhibits a metamagnetic (MM) transition at $H_{MM} = 3.5$ T. In case of $H \| c$ the magnetisation increases linearly up to 7 T. The same AFM to MM transition was found at 0.5 T in EuFe$_2$As$_2$ where it was found to be due to the reorientation of the Eu spin. We found that replacing Fe with Co strengthens the coupling between the Eu moments resulting in a higher $T_N$ and H$_{MM}$. [Preview Abstract] |
Thursday, March 24, 2011 12:39PM - 12:51PM |
W26.00006: High Magnetic Field Studies of Pressure-induced Superconductor EuFe$_2$As$_2$ Nobuyuki Kurita, Motoi Kimata, Kota Kodama, Atsushi Harada, Hiroyuki Suzuki, Takehiko Matsumoto, Shinya Uji, Taichi Terashima, Keizo Murata We have performed resistivity and susceptibility measurements of the pressure-induced superconductor EuFe$_2$As$_2$ under high magnetic fields up to 27 T. The upper critical field $B_{c2}$ and its pressure evolution up to 3.2 GPa were determined in a wide temperature range down to 1.6 K. At 2.5 GPa, nearly the optimal pressure with $T_c$=30 K, $B_{c2}$(0) obtained by the onset of resistive transitions are 25 T and 22 T for $B\parallel ab$ and $B\parallel c$, respectively, which are appreciably smaller than those for other Fe-based superconductors with similar $T_c$. The small $B_{c2}$(0) values and the peculiar $B_ {c2}$($T$) curves in EuFe$_2$As$_2$ can be explained by a multiple pair-breaking model including the exchange field due to the magnetic Eu$^{2+}$ moments. We will also present the results of quantum oscillations observed above the optimal pressure. [Preview Abstract] |
Thursday, March 24, 2011 12:51PM - 1:03PM |
W26.00007: Pressure shift of the superconducting T$_{c}$ of (Pr$_{1-x }$Sr$_{x})$FeAsO and Sm(O$_{1-x}$F$_{x})$FeAs Kalyan Sasmal, G. Mu, H.-H. Wen, B. Lorenz, Ching-Wu Chu Pressure plays important role in discovery and unraveling physics of novel superconductors.High Tc iron-based layered compounds can be obtained by hole/electron-doping.To determine if a symmetry between electron and hole-doping exists,we investigated pressure-induced shift in T$_{c}$ by carryingout resistivity measurements under hydrostatic pressure on hole-doped Pr$_{1-x }$Sr$_{x}$FeAsO up to 1.8GPa using piston-cylinder clamp cell device.The coexistence of superconductivity {\&} spin-density wave behavior were observed and pressure effects on both being investigated. Four probe resistance measurements show T$_{c}$ increases (+dT$_{c}$/dP) with pressure for under-doped Pr$_{1-x}$Sr$_{x}$FeAsO similar to high-T$_{c}$ cuprates. High pressure can compress crystalline structure of material and force its layers to be closer,which might increase material's T$_{c}$ by improving pressure-induced charge transfer between (Fe$_{2}$As$_{2})$ and (Pr/Sr)O layers. The pressure effect on T$_{c}$ of Pr$_{1-x }$Sr$_{x}$FeAsO is being compared with that of electron doped Sm(O$_{1-x}$F$_{x})$FeAs. The results suggest a symmetry appear to exist between electron and hole-doping Fe-pnictide superconductors. [Preview Abstract] |
Thursday, March 24, 2011 1:03PM - 1:15PM |
W26.00008: Pressure induced superconductivity in LaFeAsO: the role of anionic height and magnetic ordering Ravhi Kumar, James Hamlin, Yuming Xiao, Stanislav Sinogeikin, Paul Chow, Brian Maple, Yusheng Zhao, Andrew Cornelius We have investigated the pressure effect on the crystal structure and magnetic ordering of LaFeAsO at low emperature ($\sim $18K) using high pressure powder x-ray diffraction (HPXRD) and nuclear forward scattering (NFS) to pressures up to 40 GPa. We demonstrate a continuous suppression of the long range antiferromagnetic ordering in this compound under pressure. Furthermore we show here a direct correlation between the pressure induced changes in the anionic height parameter to the transition temperature (\textit{Tc}) and is first observed in the 1111 class of iron arsenide compounds under pressure. Our findings suggest that pressure induced suppression of magnetic ordering and the anionic height variation both play important roles in the origin of pressure induced superconductivity in LaFeAsO. [Preview Abstract] |
Thursday, March 24, 2011 1:15PM - 1:27PM |
W26.00009: The Pressure Effects on SmFeAsO$_{0.85}$ and PrFe$_{0.925}$Co$_{0.075}$AsO Superconductors X.L. Dong, W. Lu, J. Yang, W. Yi, Z.C. Li, C. Zhang, Z.A. Ren, G.C. Che, L.L. Sun, F. Zhou, X.J. Zhou, Z.X. Zhao We have measured magnetic susceptibility of iron pnictide superconductors SmFeAsO$_{0.85}$ and PrFe$_{0.925}$Co$_{0.075}$AsO under hydrostatic pressure up to 1.15 GPa. Our results indicate that the pressure dependences of T$_{C}$ and superfluid density in both systems are positively correlated which suggests that these quaternary iron-based superconductors are not conventional BCS ones. [Preview Abstract] |
Thursday, March 24, 2011 1:27PM - 1:39PM |
W26.00010: Valence change of europium and its relation to superconductivity in EuFe$_2$As$_{1.4}$P$_{0.6}$ and compressed EuFe$_2$As$_2$ Liling Sun, Jing Guo, Genfu Chen, Xianhui Chen, Xiaoli Dong, Wei Lu, Chao Zhang, Zheng Jiang, Yang Zuo, Shuo Zhang, Yuying Huang, Qi Wu, Xi Dai, Yuanchun Li, Jing Liu, Zhongxian Zhao Superconductivity can be realized in Eu-containing pnictides by applying chemical (internal) and physical (external) pressure, the intrinsic physical mechanism of which attracts much attention in the studies of pnictide superconductors. Here we present the experimental evidence for the pressure-induced valence change of europium in EuFe$_{2}$As$_{1.4}$P$_{0.6}$ exposed to ambient pressure and EuFe$_{2}$As$_{2}$ to high pressure by x-ray absorption measurements on L$_{3}$-Eu edge. We found that the absorption spectrum of EuFe$_{2}$As$_{1.4}$P$_{0.6}$ showed a clear spectra weight transfer from divalent to trivalent state. Furthermore, a similar behavior of valence transition as in EuFe$_{2}$As$_{1.4}$P$_{0.6}$ was also observed in EuFe$_{2}$As$_{2}$ when pressure was applied. This is the first to report the observation of valence change in pnictide superconductors and the analysis of its influence on superconductivity in EuFe$_{2}$As$_{1.4}$P$_{0.6}$ and compressed EuFe$_{2}$As$_{2}$. [Preview Abstract] |
Thursday, March 24, 2011 1:39PM - 1:51PM |
W26.00011: Pressure effects on strained FeSe$_{0.5}$Te$_{0.5}$ thin films Melissa Gooch, Bernd Lorenz, SunXiang Huang, Chia-Ling Chien, Paul Chu FeSe is the simplest structure in the family of the iron pnictides, with a reported superconducting transition of 8K for the $\alpha$-PbO- type structure. With the substitution of Te for Se, FeSe$_{0.5}$Te$_{0.5}$, was found to have an increased superconducting transition up to 15.2 K. To investigate the strain effect on the superconducting properties of the FeSe$_{0.5}$Te$_{0.5}$, thin films were grown under different conditions. The Tc and the normal state properties show a correlation to the induced strain of the system. The application of external pressure resulted in an increase of T$_c$, but at different rates depending on the pre-existent strain in the system. [Preview Abstract] |
Thursday, March 24, 2011 1:51PM - 2:03PM |
W26.00012: Enhanced SDW transition temperature under hydrostatic pressure in Fe1.02Se0.10Te0.90 Naoyuki Katayama, Kazuyuki Matsubayashi, Juscelino Leao, Sungdae Ji, Sung Chang, Yoshiya Uwatoko, Taku Sato, Seunghun Lee We will present the spin glass (SG) to spin density wave (SDW) transition in Fe1.02Se0.10Te0.90 under hydrostatic pressure. At ambient pressure, the present compound shows SG transition, characterized by a broad weak magnetic peak. By applying hydrostatic pressure, SG develops to SDW at Pc $\sim $ 0.5 GPa and the sharp strong magnetic Bragg peak appears. The SDW transition temperature is increased up to $\sim $ 250 K at 8 GPa, which is sharply contrast to the results of pressure experiments in LaFeAsO families and BaFe2As2 families. [Preview Abstract] |
Thursday, March 24, 2011 2:03PM - 2:15PM |
W26.00013: Competition between magnetic order and superconductivity in Fe oxy-pnictides Samuele Sanna, P. Carretta, G. Prando, A. Rigamonti, R. De Renzi, T. Shiroka, G. Lamura, M. Putti, A. Martinelli, R. Cimberle, M. Tropeano, C. Ferdeghini, A. Palenzona We have microscopically investigated the interplay between
magnetism (M) and superconductivity (SC) of the RFeAsO (1111)
oxy-pnictide for R=La, Sm and Ce as a function of F doping,
isoelectronic Fe/Ru substitution and external pressure. In
contrast to earlier data, our results suggest a unique
behaviour in different 1111 families at the M-SC crossover,
showing a sharp crossover between the two types of order as a
function of F doping [1-3]. In the optimally e$^-$-doped SmFe$_
{1-x}$Ru$_x$AsO$_{0.85}$F$_{0.15}$ compound, magnetic order
appears in the FeAs layers for $0.1 |
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