Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Z35: Focus Session: Iron Pnictides and Other Novel Superconductors XVII: Similar Materials: Selenides and Tellurides |
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Sponsoring Units: DMP Chair: Jiangping Hu, Purdue University Room: 405 |
Friday, March 20, 2009 11:15AM - 11:27AM |
Z35.00001: Poperties of iron selenide single crystals Cedomir Petrovic, Rongwei Hu Single crystals of FeSe were grown by molten metallic flux technique. Synchrotron powder X-ray diffraction confirms phase purity. Thermodynamic, magnetic and electrical transport properties will be presented. [Preview Abstract] |
Friday, March 20, 2009 11:27AM - 11:39AM |
Z35.00002: Single crystal growth and anisotropy of magnetic and transport properties of FeTe and FeTe1-xSx superconductors Rongwei Hu, Cedomir Petrovic Single crystals of FeTe and FeTe1-xSx were grown by molten metallic flux technique. Synchrotron powder X-ray diffraction confirms phase purity. We will present anisotropy of magnetic and electrical transport properties in normal and superconducting state of these compounds. [Preview Abstract] |
Friday, March 20, 2009 11:39AM - 11:51AM |
Z35.00003: New Fe-based superconductor S doped FeTe using nontoxic elements Yoshihiko Takano, Yoshikazu Mizuguchi Discovery of Fe-based new superconductor was received with considerable surprise. The Fe based-superconductor is expected to be a new series of high-Tc superconductors such as cuprate High-Tcs. However, one of the demerit of Fe based-superconductor is that it contains toxic element of As or Se. So, new Fe based- superconductors composed of nontoxic elements were required. Recently, we have discovered S doped FeTe as a new superconductor using nontoxic elemtns. Its superconductong transition temperature is around 10K and the upper critical fields is ~70T. This material has merit for superconducting applications. [Preview Abstract] |
Friday, March 20, 2009 11:51AM - 12:03PM |
Z35.00004: Superconducting and magnetic properties of Fe-Se-Te compounds C.V. Tomy, G. Balakrishnan, M.R. Lees The discovery of a new Fe based superconductor $\alpha $-FeSe$_{x}$ with a T$_{c}$ of 8~K, hot on the heels of the discovery of superconductivity in LaOFeP/As compounds, has triggered a fresh interest in the study of Fe based superconductors. Se can be replaced with Te in FeSe$_{1-x}$Te$_{x}$ and this results in an increase in T$_{c}$ from 8~K for x = 0 to 15~K for x = 0.5 while compounds for x $>$ 0.8 are no longer superconducting. We report the synthesis and characterization of the compounds FeSe$_{1-x}$Te$_{x}$ covering the entire solid solution range. The superconducting transition in resistivity measurements does not show any broadening in magnetic fields up to 9~T, but shifts to lower temperatures linearly with a value $\sim $ -0.22~K/T. This results in extremely high upper critical fields (H$_{c2})$ of the order of 70-80~T in these compounds. The superconducting properties are also sensitive to applied pressure and exhibit a positive dT$_{c}$/dP of around 0.41~K/kbar for the x = 0.5 composition. We observe a jump in specific heat at T$_{c}$ corresponding to a superconducting gap of 1.8~meV, indicating the bulk nature of superconductivity. Detailed investigations through magnetization, transport and specific heat measurements are presented. A study of the magnetic properties of the non superconducting end compound, FeTe is also presented to gain insight into the onset of superconductivity in the doped systems. [Preview Abstract] |
Friday, March 20, 2009 12:03PM - 12:15PM |
Z35.00005: High Pressure Structure and Transport Properties of the FeSe$_{0.88}$ Superconductor T. Wu, Z. Chen, T.A. Tyson, Z. Qin, T. Zhou, C. Zhang, S.-W. Cheong The structure of FeSe$_{0.88}$ was measured for pressures up to 7 GPa using diamond anvil cells in order to probe the changes in the lattice which coincide with change in the transport properties. These measurements are being complement by high pressure transport measurement over the same pressure range. The trends in structure and transport with pressure will be presented in order to under stand the origin of the strong pressure dependence of the superconducting transition temperature. [Preview Abstract] |
Friday, March 20, 2009 12:15PM - 12:27PM |
Z35.00006: Superconductivity and antiferromagnetism in Fe(Se$_{1-x}$Te$_x$)$_{0.82}$ E.K. Vehstedt, M.H. Fang, B. Qian, T.J. Liu, L. Spinu, H.M. Pham, W. Bao, M.R. Fitzsimmons, M. Zhernenkov, Y. Qiu, Q. Huang, M.A. Green, P. Zajdel, J. Yang, Y. Liu, Z.Q. Mao The search for unconventional superconductors has been reenergized by the discovery of $T_c$ up to 56 K in FeAs type materials [1]. Revelation of the binary superconductor FeSe, $T_c \approx 8$ K [2], prompted our investigation of the phase diagram and the evolution of superconductivity and magnetism in the ternary Fe(Se$_{1-x}$Te$_x$)$_{0.82}$ ($0 \leq x \leq 1.0$) system. We discovered a new superconducting phase with $T_{c,max} = 14$ K for $0.3 < x < 1.0$. End member FeTe$_{0.82}$ is non-superconducting and exhibits incommensurate antiferromagnetic (AFM) order. The AFM order contains both linear and spiral components, propagating diagonally in the Fe tetragonal lattice, in contrast with the commensurate AFM order in FeAs-based superconductors. Superconductivity occurs when the long-range AFM order evolves into short-range correlations with the isovalent substitution of Se for Te. These findings strongly suggest that superconductivity in this system is associated with magnetic correlations, and thus may be unconventional in nature. \\ $\left[1\right]$ A. Cho, Science \textbf{320}, 870 (2008).\\ $\left[2\right]$ F. C. Hsu \textit{et al}., Proc. Natl. Acad. Sci. USA. \textbf{105}, 14262 (2008). [Preview Abstract] |
Friday, March 20, 2009 12:27PM - 12:39PM |
Z35.00007: ABSTRACT WITHDRAWN |
Friday, March 20, 2009 12:39PM - 12:51PM |
Z35.00008: Growth and superconductivity of FeSe$_{x}$ crystals Zhili Xiao*, Umesh Patel*, Suhong Yu*, Helmut Claus, Vitalii Vlasko-Vlasov, Sevda Avci*, John Schlueter, Ulrich Welp, Wai-Kwong Kwok Stimulated by the recent discovery of high temperature superconductivity in ferrous pnictides, other iron-based planar compounds have been revisited to search for superconductivity. The most promising outcome of this effort is the discovery of superconductivity in \textit{ alpha}\textbf{ - }FeSe$_{x}$ which is less toxic but has a FeSe$_{4}$ tetrahedra planar crystal sublattice similar to that consisting FeAs$_{4}$ in the oxypnictides. Investigations on the superconductivity in FeSe$_{x}$ can shed light on the superconducting mechanism in oxypnictides. We report the growth of FeSe$_{x}$ crystals through a vapor self-transport approach. Both tetragonal and hexagon shaped FeSe$_{x}$ crystals with a lateral dimension of up to a few millimeters were obtained and their superconductivity was investigated with both magnetization and resistive measurements. We systematically explored the effect of synthesis parameters such as Fe/Se ratio, sintering temperature and cooling rate on the quality of the crystals. [Preview Abstract] |
Friday, March 20, 2009 12:51PM - 1:03PM |
Z35.00009: Superconductivity and Antiferromagnetism In Fe(Te$_{1-x}$S$_x$)$_y$ System T.J. Liu, M.H. Fang, B. Qian, E.K. Vehstedt, J.H. Yang, H.M. Pham, L. Spinu, Z.Q. Mao The surprising discovery of superconductivity up to 56 K $\left[1\right]$ in FeAs based compounds has reinvigorated the search for unusual superconductors. The recently revealed FeSe superconductor $\left[2\right]$ has inspired the community to take a second look at other previously studied materials, such as FeTe. We have investigated properties of Fe(Te$_{1-x}$S$_{x}$)$_{y}$. Our results show that the solid solution of S in this system is limited, $< 30\%$. We observed superconductivity at $~ 9$ K in both polycrystalline samples Fe(Te$_{1-x}$S$_{x}$)$_{y}$ with $0 < x \leq 0.3$ and $0.86 \leq y \leq 1.1$, and single crystals with the composition Fe(Te$_{0.9}$S$_{0.1}$)$_{0.91}$. In addition, our results suggest that this superconducting phase coexists with antiferromagnetism and that the superconducting volume fraction depends on excess Fe at interstitial sites, and excess Fe suppresses superconductivity. This allows us a unique view into the important role of magnetic correlations in mediating superconducting pairing.\\ $\left[1\right]$ A. Cho, Science \textbf{320}, 870 (2008).\\ $\left[2\right]$ F. C. Hsu \textit{et al}., Proc. Natl. Acad. Sci. USA. \textbf{105}, 14262 (2008). [Preview Abstract] |
Friday, March 20, 2009 1:03PM - 1:15PM |
Z35.00010: Superconductivity of Iron Selenide Thin Films Yuefeng Nie, Erind Brahimi, Joseph Budnick, William Hines, Menka Jain, Barrett Wells Near stoichiometry FeSe films were successfully grown on MgO, SrTiO$_{3}$, and LaAlO$_{3}$ single crystal substrates using pulsed laser deposition (PLD). X-ray diffraction analysis showed that the FeSe films have a tetragonal structure on SrTiO$_{3}$ and LaAlO$_{3}$ substrates. A mixture of tetragonal and hexagonal structures was observed on MgO substrates due to the larger lattice constant misfit. The superconductivity of films exhibited a strong dependence on epitaxial strain and thickness. Thicker films ($\sim $ 100 nm and $\sim $ 200 nm) are fully relaxed and have a clear superconducting transition near that of the bulk FeSe. Thinner films ($\sim $ 50 nm) are strained. Films on nearly lattice-matched LaAlO$_{3}$ are superconducting, while films under tension on SrTiO$_{3}$ or MgO are metallic but not superconducting down to 5K. The onset temperature for superconductivity have a near linear magnetic field dependence with dH/dT = - 2.8 T/K for fields up to 9T. [Preview Abstract] |
Friday, March 20, 2009 1:15PM - 1:27PM |
Z35.00011: Crystal growth and superconductivity of new Fe-Te base materials Genda Gu, Jinsheng Wen, Zhijun Xu, 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 recently. Because As and its oxide of the Fe-As base superconducting materials is poison, it is a serious safety issue for researchers to make the bulk materials. The new Fe-Te base superconducting materials with Se doping are less toxic and safe to handle. We have grown a number of the FeTe$_{1-x}$Se$_{x}$ single crystals (x = 0$\sim $0.5) by using a modified floating-zone growth technique. The effects of the growth condition and the composition of a feed rod on the single crystal growth of FeTe$_{1-x}$Se$_{x}$ have been studied by using a floating zone machine. The single crystals of the PbO-type tetragonal structure FeTe$_{1-y}$Fe$_{y}$ (y = 0.04 to 0.08) 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. [Preview Abstract] |
Friday, March 20, 2009 1:27PM - 1:39PM |
Z35.00012: Magnetic order and structural transition in BaFe$_2$As$_2$ and $\alpha$-Fe(Se,Te) Wei Bao, Yiming Qiu, Qingzheng Huang, Mark Green, P. Zajdel, Mike Fitzsimmons, M. Zhernenkov, Minhu Fang, B. Qian, E.K. Vehstedt, Jinhu Yang, Zhiqiang Mao, Jeff Lynn, Ying Chen, T. Wu, G. Wu, Xianhui Chen We report neutron diffraction determination of magnetic structure in BaFe$_2$As$_2$ [1] and $\alpha$-Fe(Se,Te) [2], the first in both the 122 and 11-type of the Fe-based materials. The former has the ($\pi,0$) and the later $\delta$($\pi,\pi$), $\delta= 0.346$-0.5, kind of in-plane propagation vector. In both systems, the magnetic transition is accompanied by a first-order structural transition which breaks the tetragonal symmetry of the paramagnetic phase. Antiferromagnetic wavevector as well as the moment direction were determined in relation to the associated structural distortion. The fundamentally different magnetic structures in the two types of systems would stimulate further research into the relation between the Fermi surface nesting and electronic correlation effect.\\ Reference: [1] Huang et al., arxiv:0806.2776 (Phys. Rev. Lett. accepted); [2] Bao et al., arxiv:0809.2058 [Preview Abstract] |
Friday, March 20, 2009 1:39PM - 1:51PM |
Z35.00013: Se-NMR study of superconductor FeSe under pressure Satoru Masaki, Hisashi Kotegawa, Hideki Tou, Yoshikazu Mizuguchi, Yoshihiko Takano Binary FeSe with $T_{c}$=8 K shows the simplest crystal structure in iron-based superconductors recently reported. Moreover, FeSe is reported that $T_{c}$ increases with applying pressure and the effect of pressure for $T_{c}$ is attracted. Thus the study on FeSe is quite important to investigate the role of iron-network in Fe-based layer. We have carried out Se-NMR measurements under pressure in order to clarify the symmetry of superconducting gap, the magnetic properties of normal state and the origin of pressure dependence of $T_{c}$ in FeSe. In the normal state, the nuclear spin-lattice relaxation rate 1/$T_{1}$ is in proportion to temperature (Korringa relation) at absent pressure. The Korringa relation was also observed under pressure, 0.7 GPa, However the observed value of 1/$T_{1}$ at 0.7 GPa is about twice as large as that at absent pressure. Since 1/($T_{1}T)$ is proportional to the square root of the density of state at Fermi energy $D(E_{F})$, this increase of 1/$T_{1}$ suggests the increase of $D(E_{F})$ by the applying pressure. In the superconductor, 1$/T_{1}$ abruptly decreases by superconducting transition and obeys the cube of $T$ from 7 K to 1.5 K at 2 T. the reduction of 1/$T_{1}$ was also observed below 10K under pressure. The increase of $T_{c}$ by applying pressure is conformed from microscopic viewpoint. [Preview Abstract] |
Friday, March 20, 2009 1:51PM - 2:03PM |
Z35.00014: Density Functional Study of ThCr$_{2}$Si$_{2}$-type Ternary Iron Chalcogenides: TlFe$_{2}$X$_{2}$ (X = S, Se, Te) Lijun Zhang, David Singh We report density functional calculations of electronic structure, Fermi surface, and magnetism for ternary iron chalcogenides TlFe$_{2}$X$_{2}$ (X = S, Se, Te). TlFe$_{2}$S$_ {2}$ and TlFe$_{2}$Se$_{2}$ were experimentally synthesized with the ThCr$_{2}$Si$_{2}$-structure, which consist of alternated Fe-X and electron-doping Tl layers, very similar to ternary BaFe$_{2}$As$_{2}$ system. As in all the Fe-based superconductors, the electronic structure near the Fermi level is dominated by Fe 3{d} states, with a pseudogap. Tl occurs with valence Tl${^+}$, and thus provides heavy electron-doping with 0.5 additional carrier per Fe relative to Fe-X layers. This pushes the Fermi level to the upper edge of the pseudogap and results in disappearance of hole cylinders of Fermi surface at zone center. As expected, the spin density wave instability is completely suppressed and the checkboard antiferromagnetism becomes the favored magnetic order. This over-doped system may be helpful in elucidating the magnetic order, superconducting mechanism, and spin pseudogap behavior in Fe-based materials. Tl deficiency is predicted to reinstate the part of hole Fermi surface and again induce spin fluctuations corresponding to the spin density wave, which are essential for pairing states in Fe- based superconductors. [Preview Abstract] |
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