Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session J39: Focus Session: Iron Based Superconductors: Properties and Pressure |
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Sponsoring Units: DCMP DMP Chair: M McGuire, Oak Ridge National Laboratory Room: F150 |
Tuesday, March 16, 2010 11:15AM - 11:27AM |
J39.00001: Superconducting properties of S-substituted FeTe Yoshikazu Mizuguchi, Keita Deguchi, Shunsuke Tsuda, Takahide Yamaguchi, Yoshihiko Takano Iron-chalcogenide superconductors attract us as the simplest iron-based superconductor. Tetragonal FeSe is a superconductor with a transition temperature $T_{c} \quad \sim $10 K. The $T_{c}$ dramatically increases to 37 K under pressure above 4 GPa. While FeSe exhibits superconductivity without any chemical substitution, FeTe that has a structure analogous to FeSe undergoes magnetic and structural phase transition around 70 K and does not show superconductivity. We found that S substitution for the Te site suppresses the magnetic ordering and induces superconductivity at $T_{c}$ $\sim $10 K. Recently we observed a dramatic change of superconducting property for the FeTe$_{1-x}$S$_{x}$ sample exposed to the air. Both the $T_{c}$ and the superconducting volume fraction were enhanced by the air exposure. We will discuss the factor that induces the dramatic change in FeTe$_{1-x}$S$_{x}$. [Preview Abstract] |
Tuesday, March 16, 2010 11:27AM - 11:39AM |
J39.00002: High Pressure Superconductivity and Amorphization in Iron Chalcogen Fe(Se$_{0.5}$Te$_{0.5})$ to 70 GPa A.K. Stemshorn, G.M. Tsoi, Y.K. Vohra, S.T. Weir Superconductivity and structural phase transitions in Iron-based layered superconductor Fe(Se$_{0.5}$Te$_{0.5})$ has been studied to high pressures of 70 GPa and temperature of 10 K using designer diamond anvils and x-ray diffraction using a synchrotron source. Four probe electrical resistance measurements show onset of superconductivity (T$_{c})$ at 14 K at ambient pressure with T$_{c}$ increasing with increasing pressure to 19 K at a pressure of 3.6 GPa. At higher pressures beyond 3.6 GPa, T$_{c}$ decreases and extrapolation suggests non superconducting behavior above 10 GPa. X-ray diffraction studies at room temperature show transformation from ambient pressure tetragonal phase to an amorphous phase above 11 GPa and the amorphous phase remains stable till the highest pressure of 70 GPa. The amorphous phase is observed to revert back to the parent tetragonal PbO structure upon decreasing pressure. [Preview Abstract] |
Tuesday, March 16, 2010 11:39AM - 11:51AM |
J39.00003: Crystal and electronic structure of FeSe at high pressure and low temperature Yi Zhang, Ravhi Kumar, Stanislav Sinogeikin, Yuming Xiao, Sathish Kumar, Paul Chow, Andrew Cornelius, Changfeng Chen The crystal and electronic structure of FeSe at high pressure and low temperature has been identified by density functional theory (DFT) calculations and high resolution synchrotron powder x-ray diffraction. Our results demonstrate that the HPLT phase of FeSe is orthorhombic $Pbnm$. A sluggish phase transition from $Cmma$ to $Pbnm$ occurs at low temperature over a large pressure range of 9 GPa to 23 GPa where both phases coexist. Our calculations suggest that the distorted $Cmma$ rather than the $Pbnm$ phase is responsible for the reported pressure-induced T$_c$ enhancement in FeSe. These results establish a clear picture about structural and electronic phase transitions in FeSe at HPLT and their relationships with superconductivity. [Preview Abstract] |
Tuesday, March 16, 2010 11:51AM - 12:03PM |
J39.00004: Uniaxial Pressure Measurements on Single-Crystal CaFe$_2$As$_2$ Scooter Johnson, Justin Young, Sung Hyuk Song, Rena Zieve, Adam Dioguardi, Nick Curro, Ni Ni, Sergey Bud'ko, Paul Canfield Measurements of single crystal CaFe$_2$As$_2$ have uncovered a variety of phases spanning a large range of temperatures, which makes them an interesting and important material for sorting out competing influences on strongly correlated phases. Uniaxial pressure measurements give insight into the role of dimensionality and hybridization. We apply uniaxial c-axis pressure to a single-crystal sample of CaFe$_2$As$_2$, mounted between stainless steel pressure spacers within an ac susceptibility coil. This setup is located at the base of an Oxford dilution refrigerator modified specifically for uniaxial pressure measurements. We find that a very small applied pressure, less than 0.1 kbar, induces a superconducting phase near 7K, with a transition temperature that varies little as pressure is increased further. We also find a second, strongly pressure-dependent transition near 3K. This transition temperature reaches a maximum at a pressure slightly over 1 kbar. These measurements demonstrate the sensitivity of CaFe$_2$As$_2$ to uniaxial pressure, as well as mapping out parts of its unusual phase diagram. [Preview Abstract] |
Tuesday, March 16, 2010 12:03PM - 12:15PM |
J39.00005: Relation of structure, magnetism, doping and pressure in AFe$_{2-x}$T$_x$As$_2$ (T=Co,Rh,Ru) Helge Rosner, Walter Schnelle, Deepa Kasinathan, Miriam Schmitt, Ulrich Schwarz, Michael Nicklas, Christoph Geibel, Andreas Leithe-Jasper We present an overview of our recent investigations on the SrFe$_{2-x}$T$_x$As$_2$ (T = Co, Ru, Rh) compounds. In our joint experimental and theoretical study, we report the influence of hydrostatic pressure and substitution at the Fe site on the magneto-structural and superconducting transitions. The magnetism is weakened upon the application of pressure as indicated by resistivity, X-ray data and density functional band structure calculations. Similar to substitution on the Sr site, substitutions on the Fe-site quench the magnetic transition and induce bulk superconductivity with $T_c$ up to 20 K for ambient pressure and up to 27 K for underdoped SrFe$_{2-x}$Co$_x$As$_2$ for pressures of 2.6GPa. In our analysis, we attempt to disentangle the interplay of charge doping and structural changes induced by the substitution and by external pressure. [Preview Abstract] |
Tuesday, March 16, 2010 12:15PM - 12:27PM |
J39.00006: Superconductivity in pure and Co-doped BaFe$_2$As$_2$ under high pressure E. Colombier, S. Kim, N. Ni, A. Thaler, S. L. Bud'ko, P. C. Canfield, M. S. Torikachvili In-plane resistivity of pure and Co-doped BaFe$_2$As$_2$ single crystals was measured up to $\sim 75$ kbar in liquid media using piston-cylinder ($P < 25$ kbar) and modified Bridgman ($P < 75$ kbar) pressure cells. A dome-like rigeon of superconductivity with $T_c^{max}$ at $\sim 55$ kbar was induced in pure BaFe$_2$As$_2$. Dome-like $T_c(P)$ behavior was also observed for underdoped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. For overdoped samples $T_c$ decrease under pressure, followed by filamentary superconductivity, was measured. The evolution of the pressure dependencies of the normal state resistivity, initial $dT_c/dP)$, maximum $T_c$ observed under pressure, with Co doping will be discussed. [Preview Abstract] |
Tuesday, March 16, 2010 12:27PM - 12:39PM |
J39.00007: Superconductivity in CaFe$_{2}$As$_{2}$ under uniaxial pressure: new insights from neutron diffraction experiments K. Proke\v{s}, A. Kreyssig, B. Ouladdiaf, D.K. Pratt, N. Ni, S.L. Bud'ko, P.C. Canfield, R.J. McQueeney, D.N. Argyriou, A.I. Goldman CaFe$_{2}$As$_{2}$, a member of the 122 iron arsenide family, is not superconducting at ambient pressure. It undergoes structural and antiferromagnetic transitions at $T_{TO}$ = 172 K that are strongly coupled [1]. In clamped cell pressure measurements using a liquid medium, superconductivity has been observed with $T_{C}$ as high as 12 K [2]. However, measurements using a He-gas pressure cell, where non-hydrostatic pressure components are minimized show no evidence of superconductivity [3]. We report on neutron diffraction experiments using CaFe$_{2}$As$_{2 }$single crystals under uniaxial pressure applied along the $c$ axis. We find that, above 0.05 GPa, several structural phases coexist at low temperature. Simultaneous diffraction/resistivity measurements strongly suggest that a pressure-stabilized tetragonal phase is responsible for the superconductivity in CaFe$_{2}$As$_{2}$. -- The work at Ames Laboratory was supported by US DOE (DE-AC02-07CH11358). [1] A.I. Goldman, et al., PRB \textbf{78} (2008) 100506. [2] M.S. Torikachvili, et al., PRL \textbf{101} (2008) 057006. [3] W.Yu, et al., PRB \textbf{79} (2009) 020511. [Preview Abstract] |
Tuesday, March 16, 2010 12:39PM - 12:51PM |
J39.00008: High Pressure Kondo-like Behavior in Quaternary Rare Earth Transition Metal Arsenide Oxide W.O. Uhoya, G.M. Tsoi, Y.K. Vohra, S.T. Weir, M.A. McGuire, A.S. Sefat, B.C. Sales, D.G. Mandrus High pressure electrical resistance studies at low temperatures have been performed on a quaternary rare earth transition metal arsenide oxide (NdCoAsO) to 70 GPa and a temperature of 10 K using designer diamond anvils. A resistance minimum at low temperatures exhibiting Kondo-like behavior was observed at temperature T$_{K }$= 17 K at ambient pressure. The Kondo temperature was observed to increase with increasing pressure and rising to 30 K at a pressure of 70GPa. High pressure x-ray diffraction studies were performed using a synchrotron source to a pressure of 35 GPa at ambient temperature. The ambient pressure tetragonal phase (P4/nmm, Z = 2) was observed to transform to a low-symmetry phase at a pressure of 27 GPa. The Kondo-like behavior was observed to persist in NdCoAsO to the highest pressure and the superconducting transition was not observed to a pressure of 70 GPa. [Preview Abstract] |
Tuesday, March 16, 2010 12:51PM - 1:03PM |
J39.00009: Electrical resistivity of CeFeAsO and CeFePO under pressure D.A. Zocco, R.E. Baumbach, J.J. Hamlin, M. Janoschek, I.K. Lum, M.B. Maple, M.A. McGuire, A.S. Sefat, B.C. Sales, R. Jin, D. Mandrus, J.R. Jeffries, S.T. Weir, Y.K. Vohra The strongly correlated electronic properties of CeFeAsO and CeFePO iron pnictide compounds were studied via electrical transport measurements under high-pressure, using piston-cylinder, Bridgman-anvil and designer-diamond-anvil cell techniques. The temperature-pressure phase diagram of CeFeAsO polycrystals revealed that after an initial decrease of the ordering temperature of the Fe magnetic moments and an increase of the antiferromagnetic ordering (N\'{e}el) temperature of the Ce magnetic moments, the magnetic phases involving the Fe and Ce ions coexist up to 15 GPa, with no signs of pressure-induced superconductivity up to 50 GPa. For the CeFePO single crystals, pressure seemed to further stabilize the Kondo screening of the Ce 4$f$-electron magnetic moments. [Preview Abstract] |
Tuesday, March 16, 2010 1:03PM - 1:15PM |
J39.00010: Pressure-induced Competition between Superconductivity and Kondo Effect in CeFeAsO$_{1-x}$F$_{x}$ (x=0.16 and 0.3) Liling Sun, Xi Dai, Genfu Chen, Nanlin Wang, Zhian Ren, Xiaoli Dong, Qi Wu, Hong Ding, Zhongxian Zhao We studied high-pressure behavior of CeFeAsO$_{1-x}$F$_{x}$ superconductors with x=0.16 and x=0.3 by the \textit{in-situ} measurements of electrical resistance, x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) in a diamond anvil cell. A pressure-induced quantum phase transition from the superconducting state to the non-superconducting Kondo screened phase associated with a volume collapse was discovered in the layered CeFeAsO$_{1-x}$F$_{x}$ compounds. This finding is the first observation of pressure-induced quantum phase transition from an electron pairing state in the conduction band to a Kondo screened state between conducting electrons and local moments, and reveals a physical picture of competition between Kondo singlet and BCS singlet in the Ce-pnictide superconductors. [Preview Abstract] |
Tuesday, March 16, 2010 1:15PM - 1:27PM |
J39.00011: Microscopic origin of pressure-induced phase transitions in iron pnictides Ingo Opahle, Yu-Zhong Zhang, Hem C. Kandpal, Harald O. Jeschke, Roser Valenti We have performed ab initio molecular dynamics calculations on the three materials (Ca, Sr, Ba)Fe$_2$As$_2$ under pressure. We find that the structural phase transition (orthorhombic to tetragonal symmetry) is always accompanied by a magnetic phase transition in all the compounds, while the nature of the transitions is different for the three systems. Our calculations explain the origin of the existence of a collapsed tetragonal phase in CaFe$_2$As$_2$ and its absence in BaFe$_2$As$_2$. We will also present a detailed analysis of pressure-induced superconductivity in BaFe$_2$As$_2$ based on neutron diffraction experiments, ARPES and bandstructure calculations and we will show the importance of structural distortions for the onset of superconductivity. [Preview Abstract] |
Tuesday, March 16, 2010 1:27PM - 1:39PM |
J39.00012: The structural and electronic properties of binary FeAs under pressure J.R. Jeffries, N.P. Butch, S.R. Saha, K. Kirshenbaum, J. Paglione, S.T. Weir The binary FeAs system crystallizes in the MnP-type orthorhombic (Pnam) crystal structure, and is not uncommon as an impurity phase in the growth of some ferropnictide superconductors. A transition occurs near 77 K, below which temperature FeAs displays magnetic ordering. The electronic and structural properties of FeAs are important to understanding the general phenomena associated with ferropnictide compounds, as well as interpreting the results of compounds that may contain impurities of this binary compound. We present electrical transport and structural parameters, from x-ray diffraction, of FeAs as a function of pressure up to 60 GPa using designer and conventional diamond anvil cells. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344. [Preview Abstract] |
Tuesday, March 16, 2010 1:39PM - 1:51PM |
J39.00013: Effects of chemical pressure in CaFe$_{4}$As$_{3}$ single crystals Liang Zhao, Victor Leyva, Emilia Morosan CaFe$_{4}$As$_{3}$ is a recently discovered iron pnictide compound that shows complex magnetic and transport properties. In the present study, we are tuning the chemical pressure of the lattice by partially substituting As with P. The doped single crystals show systematic changes in the critical temperatures of both the spin density wave (SDW) and the incommensurate-to-commensurate transitions: the SDW temperature is slowly moving down, while the lower transition is moving to higher temperatures with increasing amounts of P. [Preview Abstract] |
Tuesday, March 16, 2010 1:51PM - 2:03PM |
J39.00014: Magnetic Transport Properties in Pressure-Induced Superconductor EuFe$_{2}$As$_{2}$ Nobuyuki Kurita, Motoi Kimata, Kota Kodama, Hidetaka Satsukawa, Atsushi Harada, Hiroyuki Suzuki, Takehiko Matsumoto, Shinya Uji, Taichi Terashima, Keizo Murata A systematic pressure investigation of magnetoresistance and Hall effect has been performed on the antiferromagnetic compound EuFe$_{2}$As$_{2}$ which exhibits pressure-induced superconductivity ($T_{c}\sim $30 K and $P_{c}\sim $2.5 GPa). At ambient pressure, temperature dependence of Hall coefficient $R_{H}$ indicates that the dominant carrier below $T\sim $190 K ($T$: Structural and magnetic transition temperature) is electron-like. As pressure increases, both of the down-turn associated with $T$ and anomalous roll-over around 30 K in $R_{H}$ become less pronounced and shift to low temperature region. We will also refer to the temperature and field dependence of Hall angle \textit{$\theta $}$_{H}$ with applied pressures. [Preview Abstract] |
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