Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session W36: Focus Session: Fe-based Superconductors: Synthesis and Characterization |
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Sponsoring Units: DMP DCOMP Chair: Cedomir Petrovic, Brookhaven National Lab Room: 344 |
Thursday, March 21, 2013 2:30PM - 2:42PM |
W36.00001: Preparation and characterization of annealed single crystals of Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ at and near optimally doped, 0.07$\le $x$\le $0.095 G.R. Stewart, B.D. Faeth, J.S. Kim, G.N. Tam Using self flux single crystal growth and long term annealing in the presence of an As vapor source, we report resistivity, magnetic susceptibility and specific heat characterization of optimized samples at and near to optimally doped Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$. The ultimate achievable T$_{c}$ in 122 BaFe$_{2}$As$_{2}$ doped on the Fe layers will be discussed, along with the variation with composition on a very fine scale of the linear T term in the resistivity and the discontinuity in the specific heat, $\Delta $C/T$_{c}$, on both the overdoped and underdoped (coexistent with magnetism) sides of optimally doped. [Preview Abstract] |
Thursday, March 21, 2013 2:42PM - 2:54PM |
W36.00002: Properties of epitaxial Ba(Fe$_{\mathrm{1-x}}$Co$_{\mathrm{x}})_{2}$As$_{2}$ thin films on different substrates Q.Y. Lei, M. Golalikhani, A. Rafti, J. Qiu, M. Hambe, F. Williams, Q. Yang, D. Temple, E.D. Bauer, F. Ronning, Q.X. Jia, X.F. Wang, X.H. Chen, J.D. Weiss, E.E. Hellstrom, X.X. Xi We have grown epitaxial, optimally-doped superconducting Ba(Fe$_{0.92}$Co$_{0.08})_{2}$As$_{2}$ films on SrTiO$_{3}$, (La, Sr)(Al, Ta)O$_{3}$ and LaAlO$_{3}$ substrates, which have a range of lattice mismatch, and studied the strain effect on the structural and transport properties of the films. We found that the superconducting transition temperature increased as the c lattice constant decreased and a lattice constant increased. The thickness dependence of the superconducting transition temperature was studied, which was related to the strain and strain relaxation. A zero-resistance $T_{c}$ of 21.7 K was obtained in the 120 nm-thick Ba(Fe$_{0.92}$Co$_{0.08})_{2}$As$_{2}$ film on SrTiO$_{3}$ substrate. [Preview Abstract] |
Thursday, March 21, 2013 2:54PM - 3:06PM |
W36.00003: Combined effects of annealing/quenching and transition metal substitution on physical properties of CaFe$_{2}$As$_{2}$ Sheng Ran, Sergey Bud'ko, Paul Canfield Our previous work on CaFe$_{2}$As$_{2}$ single crystals grown out of FeAs flux has shown that a process of annealing and quenching can be used as an additional control parameter which can tune the ground state of CaFe$_{2}$As$_{2}$ systematically, in a manner similar to applied pressure. With combined effect of annealing/quenching and transition metal substitution, CaFe$_{2}$As$_{2}$ system offers ready access to the salient low-temperature states associated with Fe-based superconductors: antiferromagnetic/orthorhombic, superconducting, and nonmagnetic/collapsed tetragonal. In this talk we will present systematic studies of the combined effects of annealing/quenching and chemical substitution with various transition metals (Co, Ni, Rh) on the physical properties of CaFe$_{2}$As$_{2}$ and construct phase diagrams for different substitution levels and different annealing/quenching temperatures. [Preview Abstract] |
Thursday, March 21, 2013 3:06PM - 3:18PM |
W36.00004: Superparamagnetism and interfacial superconductivity in rare earth Pr-doped Ca122 L.Z. Deng, B. Lv, F.Y. Wei, Y.Y. Xue, C.W. Chu To better understand the origin of the non-bulk superconductivity with an unusually high onset-T$_{c}$ (49 K) and its superconducting behavior in the rare earth Pr-doped Ca122 [(Ca$_{1-x}$Pr$_{x})$Fe$_{2}$As$_{2}$], detailed chemical analyses and magnetization measurements on both the as-synthesized and annealed single crystals were carried out. A small but non-negligible As-deficiency and superparamagnetic clusters (SPCs) were detected in the superconducting as-synthesized crystals, suggesting that the SPCs originate from the As vacancies. The magnetic moment of the SPC were found to be insensitive to the doping level x, while the SPC density (n) is zero for x \textless 0.05 in the non-superconducting region and increases monotonically with x for x \textgreater 0.1 in the superconducting region. The superconducting volume fraction (f) was shown to be very closely related with n. Noticeable inter-cluster interactions, from antiferromagnetic for x \textless 0.05 (non -SC region) to weakly ferromagnetic for x \textgreater 0.1 (SC region) were found, suggesting that the defects are ordered. Systematically annealing the crystals over 500-920${^\circ}$ simultaneously suppress both n and f. Therefore, we propose that the ordered vacancies, and the associated interfaces, are responsible for the rather high onset-T$_{c}$. [Preview Abstract] |
Thursday, March 21, 2013 3:18PM - 3:30PM |
W36.00005: Evidence of Interface-Enhanced T$_{c}$ in Rare-Earth Doped Ca122 C.W. Chu, Bing Lv, Liangzi Deng, Fengyan Wei, Yu-Yi Xue, Melissa Gooch, Bernd Lorenz Nonbulk superconductivity with an onset-T$_{c}$ up to 49 K has been observed in single crystalline rare-earth doped CaFe$_{2}$As$_{2}$ [(Ca$_{1-x}$,RE$_{x})$122] recently. Such a T$_{c}$ is more than $\sim$ 20 K higher than any known compounds that consist of one or more of the Ca, RE, Fe and As elements at ambient or under high pressures. The unusually high onset-T$_{c}$ has therefore been attributed to interface effect. We have made systematic magnetic, transport, calorimetric and structural studies. They show: a chemically homogeneity of $\Delta $x \textless\ 0.005 over a 1$\mu$m; less than 5 {\%} of a bulk superconducting volume fraction; a doping-insensitive onset-T$_{c}$ in samples with or without the ``collapsed phase'', varying from $\sim$ 42 K for RE $=$ Nd to 49 K for RE $=$ Pr with a doping sensitive superconducting volume fraction, suggesting that the high onset-T$_{c}$ cannot be due to chemical doping or the effect of the ``collapsed phase''; an unusually high magnetic anisotropy up to 200, in contrast to the value of 4 from the sample geometric anisotropy, suggesting that the superconducting body has a very high aspect ratio; several steps in the magnetic susceptibilities along both the c- and ab-directions in the field range between 10$^{-3}$ to 10$^{+3}$ Oe, demonstrating the sample consisting of Josephson-Coupled superconducting islands imbedded with nano-scale interfaces; and the presence of superparamagnetic clusters associated with minute As-vacancies, consistent with theoretical calculations. The present studies therefore present the strongest evidence for interface-enhanced T$_{c}$ to date. [Preview Abstract] |
Thursday, March 21, 2013 3:30PM - 3:42PM |
W36.00006: Films of Iron-Chalcogenide Superconductors and Applications Qiang Li, Weidong Si Iron chalcogenides are of great interest for both basic physics and applications. Although their superconducting transition temperatures are typically lower than those of iron pnictides, iron chalcogenides exhibit lower anisotropies with very high upper critical field slopes near the superconducting transition temperatures. In this presentation, I will discuss recent progress in the superconducting thin films and coated conductors of iron chalcogenides. The very high upper critical fields and critical current densities of these films suggest that they are prospective candidates for high field and energy applications. - Reference: Qiang Li, Weidong Si, and Ivo Dimitrov, ``Films of Iron-Chalcogenide Superconductors,'' Rep. Prog. Phys. \textbf{74} 124510 (2011) [Preview Abstract] |
Thursday, March 21, 2013 3:42PM - 3:54PM |
W36.00007: Plused Laser Deposition growth of iron chalcogenide with tunable structural and physical properties Wangdong Kong, Jun Ma, Lei Yan, Hong Ding Since the discovery of iron superconductor in 2008, plenty of spectroscopic experimental and theoretical works have been done to explore the mechanism of superconductivity. In parallel, much effort is devoted to thin film growth with the aim to fabricate high quality samples with tunable structural and physical properties,as well as for the development of new functional devices. Here we apply the Plused Laser Deposition (PLD) method to obtain iron chalcogenide superconductor thin films. By adjusting the growth parameters and procedure, we can modulate the structure and properties of the thin films. One of the main results is the enhancement of Tc. We are constructing a new system combining ARPES and PLD for in-situ measurements which will surely shed interesting light on the mechanism of superconductivity. [Preview Abstract] |
Thursday, March 21, 2013 3:54PM - 4:06PM |
W36.00008: Effects of Oxygen Annealing in Fe(Te,Se) Single Crystals Tsuyoshi Tamegai, Yue Sun, Toshihiro Taen, Yuji Tsuchiya, ZhiXiang Shi Iron-chalcogenide superconductor Fe(Te,Se) has the simplest structure among all iron-based superconductors. Yet, its superconducting properties except for $T_{\mathrm{c}}$ are not very much reproducible. This is partly due to the fact that the as-grown crystals of Fe(Te,Se) is not superconducting, and post-annealing is important to induce superconductivity. We found that the annealing in a controlled oxygen atmosphere is very important to induce superconductivity in this system. Upon annealing in oxygen atmosphere, the content of excess iron in the crystal decreases. We will demonstrate the dynamics of the oxygen annealing process by changing the annealing time and temperature. We also compare the effect of different annealing conditions, such as vacuum annealing, with that of oxygen annealing. Finally, physical properties of well-characterized Fe(Te,Se) crystals are discussed together with the vortex physics in this system. [Preview Abstract] |
Thursday, March 21, 2013 4:06PM - 4:18PM |
W36.00009: The mechanism of alcoholic beverage induced superconductivity in Fe-chalcogenide compounds Keita Deguchi, Satoshi Demura, Hiroyuki Okazaki, Saleem Denholme, Masaya Fujioka, Toshinori Ozaki, Takahide Yamaguchi, Hiroyuki Takeya, Yoshihiko Takano We have clarified the mechanism of alcoholic beverage induced superconductivity in Fe-chalcogenide compounds. Previously we reported that the bulk superconductivity in Fe-based compounds Fe(Te, Se) and Fe(Te, S) is achieved by heating in alcoholic beverages [1,2]. However, the exact mechanism of how they act to enhance the superconductivity in the compounds remains unsolved. To understand the effect of alcoholic beverage treatment, we investigated the mechanism using a technology of metabolomic analysis [3]. We found that weak acid in alcoholic beverages has the ability to deintercalate the excess Fe, which is not in favor of superconductivity. In this presentation, we will discuss the systematic mechanism to induce superconductivity in Fe-chalcogenide compounds. [1] K. Deguchi et al., Supercond. Sci. Technol. 24 (2011) 055008. [2] K. Deguchi et al., arXiv: 1210.5889. [3] K. Deguchi et al., Supercond. Sci. Technol. 25 (2012) 084025. [Preview Abstract] |
Thursday, March 21, 2013 4:18PM - 4:30PM |
W36.00010: Improved growth of Ln1111 superconducting crystals from NaAs/KAs flux Nikolai D. Zhigadlo, S. Weyeneth, S. Katrych, P.J.W. Moll, K. Rogacki, S. Bosma, R. Puzniak, J. Karpinski, B. Batlogg Single crystals of the LnFeAsO (Ln1111, Ln $=$ Pr, Nd, and Sm) family with lateral dimensions up to 1 mm were grown from NaAs and KAs flux using the cubic anvil high-pressure and high-temperature technique. The crystals become superconducting when O is partially substituted by F (PrFeAsO$_{\mathrm{1-x}}$F$_{\mathrm{x}}$ and NdFeAsO$_{\mathrm{1-x}}$F$_{\mathrm{x}})$ or when Fe is substituted by Co (SmFe$_{\mathrm{1-x}}$Co$_{\mathrm{x}}$AsO). In SmFe$_{\mathrm{1-x}}$Co$_{\mathrm{x}}$AsO the maximum $T_{\mathrm{c\thinspace }}$is 16.3 K for x $=$ 0.8. From transport and magnetic measurements we estimate the critical fields and their anisotropy, and we find these superconducting properties to be quite comparable to the ones in SmFeAsO$_{\mathrm{1-x}}$F$_{\mathrm{x}}$ with a much higher $T_{\mathrm{c}}$ of $\approx $ 50 K. The magnetically measured critical current densities are as high as 10$^{\mathrm{9}}$ A/m$^{\mathrm{2}}$ at 2 K up to 7 T, with indications of the usual ``fish tail'' effect. [Preview Abstract] |
Thursday, March 21, 2013 4:30PM - 4:42PM |
W36.00011: Synthesis methods and character of iron-based mixed-anion superconductor with suppression of the amorphous FeAs impurity phase Masaya Fujioka, Toshinori Ozaki, Hiroyuki Okazaki, Denholme Saleem, Keita Deguchi, Satoshi Demura, Hiroshi Hara, Tohru Watanabe, Hiroyuki Takeya, Takahide Yamaguchi, Hiroaki Kumakura, Yoshihiko Takano To obtain the high superconducting properties of polycrystalline SmFeAsO$_{\mathrm{1-x}}$F$_{\mathrm{x}}$, we investigated the following three synthesis methods: a high pressure synthesis, a low temperature synthesis with gradual cooling and a metal added synthesis. Generally, polycrystalline SmFeAsO$_{\mathrm{1-x}}$F$_{\mathrm{x}}$ is composed of superconducting grains and a little amorphous FeAs compounds. These areas randomly co-exist and amorphous areas are located between the superconducting grains. Therefore, we suggest that the superconducting current is prevented by the amorphous areas. In fact, although the single crystal of this material shows a large critical current density of 10$^{\mathrm{6}}$ A/cm$^{\mathrm{2}}$, polycrystalline SmFeAsO$_{\mathrm{1-x}}$F$_{\mathrm{x}}$ shows a significant depression of critical current density due to this grain boundary blocking effect. To obtain a high global critical current density, it is important to investigate how to remove the amorphous FeAs. It is found that the impurity phase of amorphous FeAs is decreased by using the above three synthesis methods. [Preview Abstract] |
Thursday, March 21, 2013 4:42PM - 4:54PM |
W36.00012: Hydrostatic and chemical pressure tuning of CeFeAs$_{1-x}$P$_x$O single crystals: The intriguing interaction between 3$d$- and 4$f$-correlations M. Nicklas, K. Mydeen, E. Lengyel, A. Jesche, C. Geibel We present a combined P-substitution and hydrostatic pressure study on CeFeAs$_{1-x}$P$_{x}$O single crystals in order to investigate the peculiar relationship of the local moment magnetism of Ce, the ordering of itinerant Fe moments, and their connection with the occurrence of superconductivity [1,2]. Our results evidence a close relationship between the weakening of Fe magnetism and the change from antiferromagnetic to ferromagnetic ordering of Ce moments at $p^*=1.95$ GPa in CeFeAs$_{0.78}$P$_{0.22}$O. The absence of superconductivity in CeFeAs$_{0.78}$P$_{0.22}$O and the presence of a narrow and strongly pressure sensitive superconducting phase in CeFeAs$_{0.70}$P$_{0.30}$O and CeFeAs$_{0.65}$P$_{0.35}$O indicate the detrimental effect of the Ce magnetism on superconductivity in P-substituted CeFeAsO.\\[4pt] [1] A. Jesche, T. F\"orster, J. Spehling, M. Nicklas, M. de Souza, R. Gumeniuk, H. Luetkens, T. Goltz, C. Krellner, M. Lang, J. Sichelschmidt, H.-H. Klauss, and C. Geibel, Phys. Rev. B 86, 020501(R) (2012).\\[0pt] [2] K. Mydeen, E. Lengyel, A. Jesche, C. Geibel, and M. Nicklas, Phys. Rev. B 86, 134523 (2012). [Preview Abstract] |
Thursday, March 21, 2013 4:54PM - 5:06PM |
W36.00013: Raman spectroscopic analysis for grain boundary of Superconducting polycrystalline SmFeAsO$_{\mathrm{1-x}}$F$_{\mathrm{x}}$ Hajime Shinohara, Masaya Fujioka, Hiroki Taniguchi, Mitsuru Itoh, Toshiyuki Atou, Yoshihiko Takano, Hiroaki Kumakura, Masanori Matoba, Yoichi Kamihara The observation of grain boundary structures is essential technique to fabricate high-T$_{\mathrm{c}}$ superconducting wires. Spatial crystal distribution analysis for grain boundary of superconducting polycrystalline SmFeAsO$_{\mathrm{1-x}}$F$_{\mathrm{x}}$ is demonstrated by Raman Spectroscopy. Polycrystalline SmFeAsO$_{\mathrm{1-x}}$F$_{\mathrm{x}}$ samples were synthesized using two-step solid state reaction described elsewhere [New J. Phys.\textbf{12}, 033005 (2010)]. Samples' surface and their structures were checked by microscopic optical measurement and electron beam backscattering diffraction (EBSD) analysis. The Raman spectroscopy was performed at the range from 150 cm$^{-1}$ to 500 cm$^{-1}$. F contents (x) were 0, 0.019, 0.037, 0.045, 0.069, 0.075. Although our several spectra are similar to which had been reported [Hadjiev, et al, Phys. Rev. B. \textbf{77}, 220505 (2008)], our results indicate that grain boundary structures are mixtures of small single crystalline SmFeAsO$_{\mathrm{1-x}}$F$_{\mathrm{x}}$ and amorphous-FeAs. Details of the Raman spectra will be presented at the conference. [Preview Abstract] |
Thursday, March 21, 2013 5:06PM - 5:18PM |
W36.00014: Synthesis and characterization of whisker crystals of iron-based superconductor Jun Li, Jie Yuan, Hua-Bing Wang, Kazunari Yamaura Single-crystal superconducting whiskers of Ca$_{10}$(Pt$_4$As$_8)$(Fe$_{1.8}$Pt$_{0.2}$As$_2)_5$ were grown in a Ta capsule in an evacuated quartz tube by a flux method [J. Li, \textit{et al.} J. Am. Chem. Soc. 134, 4068$-$4071 (2012)]. This technique can be potentially useful for growth of other whiskers containing toxic elements, although the growth mechanism is not understood well. The Ca$_{10}$(Pt$_4$As$_8)$(Fe$_{1.8}$Pt$_{0.2}$As$_2)_5$ whiskers were confirmed to have excellent crystallinity with $T_{\mathrm{c}}$ of 33 K, $\mu_{\mathrm{0}}H_{\mathrm{c2}}$ of 52.8 T, and $J_{\mathrm{c}}$ of 6.0 $\times$ 10$^5$ A/cm$^2$ (at 26 K). The $T_{\mathrm{c}}$ value is comparable with that of the bulk material. Since cuprate high-$T_{\mathrm{c}}$ superconducting whiskers are fragile ceramics, the present intermetallic superconducting whiskers with high-$T_{\mathrm{c}}$ have better opportunities for device applications. In addition, we studied the Ca$_{10}$(Pt$_4$As$_8)$(Fe$_{2-x}$Pt$_{x}$As$_2)_5$ superconducting whiskers consisting of several grains. With current tunneling across the grain boundaries, current-voltage characteristics show the behavior of Josephson tunnel junction effect with pronounced hysteresis. In this talk, we review the growth of the superconducting whiskers and shows progress of studies of the Josephson junction using the whiskers. [Preview Abstract] |
Thursday, March 21, 2013 5:18PM - 5:30PM |
W36.00015: Annealing and doping effects of Fe-based superconductors with thick perovskite-type blocking layers Hiraku Ogino, Akiyasu Yamamoto, Kohji Kishio, Jun-ichi Shimoyama After the discovery of superconductivity in LaFeAs(O,F), several types of Fe-based superconductors were developed. In particular, iron-based superconductors having extremely thick perovskite-type blocking layers, such as (Fe2As2)(Ca5(Sc,Ti)4Oy) and (Fe2As2)(Ca4(Mg,Ti)3Oy) were discovered[1]. Interlayer Fe-Fe distances of these compounds are from 2 to 3 nm, which are much longer than other iron-based superconductors. Antiferromagnetic ordering or structural transition is not observed in these compounds, and superconducting transitions appear without intentional carrier doping. In this study, we have investigated carrier doping and annealing effect of these compounds. Relationship between crystal structure, chemical compositions and physical properties will be discussed. [1] H. Ogino et al., Appl. Phys. Express 3 (2010) 063103 [Preview Abstract] |
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