Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session F52: Focus Session: New and Improved Superconducting Materials |
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Sponsoring Units: DMP Chair: Eric Palm, National High Magnetic Field Laboratory Room: Mile High Ballroom 1F |
Tuesday, March 4, 2014 8:00AM - 8:12AM |
F52.00001: Optimization and doping of 112 Fe pnictide single crystals Akshat Puri, Jennifer Misuraca, Jedediah K. Morris, Meigan Aronson The recent discovery of Ca$_{1-x}$La$_{x}$FeAs$_{2}$, which when doped with Sb has a T$_{c}$ of 43K, has led to an increased interest in Fe pnictides in the 112 structure [1]. We have grown plate-like single crystals of LaFe$_{0.6}$Sb$_{2}$ from a self flux. These form in a tetragonal 112 structure with many Fe vacancies, as measured by single crystal x-ray diffraction. The crystal growths were optimized in two ways. Arc melting elemental Fe granules before use resulted in larger ($\sim$ 1 cm$^{2}$) crystals, and including a rapid cool-down during the growth avoided the formation of a parasitic phase, thus increasing the yield. Doping Ni into the structure resulted in a change in the lattice constants from a = 4.4026 {\AA}, c = 10.0341 {\AA} for undoped LaFe$_{0.6}$Sb$_{2}$ to a = 4.4343 {\AA}, c = 9.8911 {\AA} for LaNiSb$_{2}$. Energy dispersive x-ray spectroscopy showed that Ni replaces Fe and also occupies the vacancies, and at 89\% Ni doping, there are no vacancies in the structure. Due to the many vacancies in undoped LaFe$_{0.6}$Sb$_{2}$, the Sb residing near the vacant sites is strongly anharmonic in character; the electronic structure changes with doping and this is seen in the parameter becoming harmonic. [1] Kudo et al. arXiv:1311.1269 (2013). [Preview Abstract] |
Tuesday, March 4, 2014 8:12AM - 8:24AM |
F52.00002: Search for Superconductivity in Extraterrestrial Materials Ivan K. Schuller, S. Gu\'enon, J.G. Ramirez, Ali C. Basaran, M. Thiemens, S. Taylor Extraterrestrial and in particular presolar materials have formed under very extreme and unconventional growth conditions. They are highly heterogeneous and they consist of an unmatched variety of chemical compounds. In order to test this materials for superconductivity, we use the very sensitive and highly selective technique of Magnetic Field Modulated Microwave Spectroscopy. The sample is placed in a microwave cavity and the microwave reflectivity is monitored in the presence of a small AC magnetic field. Among others, we have investigated micrometeorites that were extracted from the water well of the Amundsen-Scott South Pole Station and materials from the Allende and Murchinson meteorite. First results will be presented and the challenges of this research project will be discussed. [Preview Abstract] |
Tuesday, March 4, 2014 8:24AM - 8:36AM |
F52.00003: Search for Superconductivity in Cu-Chlorides and Ferromagnetism in Partially Oxidized CuCl Thomas Saerbeck, Juan Pereiro, James Wampler, Jacob Stanley, James Wingert, Oleg G. Shpyrko, Ivan K. Schuller The phase diagram of copper-halides shows a rich diversity not only in crystalline structure, but also in magnetic and electronic properties. In particular, the chemically unstable CuCl has been proposed several times as a candidate for high-temperature superconductivity. We present a search for superconductivity in systems of CuCl/Si and CuCl$_{2}$/Si, which leads to the observation of ferromagnetism with a Tc of 18 K in bulk CuCl samples [1]. The hitherto unreported magnetism is found to emerge in pure CuCl upon prolonged exposure to humid air. Magnetic field modulated microwave spectroscopy in addition to SQUID magnetometry and x-ray diffraction are used to identify phase transitions and compare them to the antiferromagnetic transitions in other Copper-chloride structures. \\[4pt] [1] T. Saerbeck, J. Pereiro, J. Wampler, J. Stanley, J. Wingert, O. G. Shpyrko, and Ivan K. Schuller, Journal of Magnetism and Magnetic Materials \textbf{346}, 161 (2013). [Preview Abstract] |
Tuesday, March 4, 2014 8:36AM - 9:12AM |
F52.00004: Superconductivity in BiS$_2$-based compounds Invited Speaker: Duygu Yazici Polycrystalline samples of $Ln$O$_{0.5}$F$_{0.5}$BiS$_2$ ($Ln$ = La, Ce, Pr, Nd, Yb) were synthesized by solid-state reaction. These compounds form in a tetragonal structure with space group $P4/nmm$ conforming to the CeOBiS$_2$ crystal structure. Electrical resistivity, magnetic susceptibility and specific heat measurements were performed on all of the samples. All of the compounds exhibit superconductivity in the range 1.9 K - 5.4 K, and the YbO$_{0.5}$F$_{0.5}$BiS$_2$ sample was also found to exhibit magnetic order (probably antiferromagnetic order) at $\sim$2.7 K that appears to coexist with superconductivity below 5.4 K [1]. Electron-doping appears to induce superconductivity in the BiS$_2$-based superconductors as partial substitution of F for O is necessary to observe superconductivity. This was further demonstrated in a study where trivalent La$^{+3}$ was partially substituted with tetravalent Th$^{+4}$, Hf$^{+4}$, Zr$^{+4}$, and Ti$^{+4}$, all of which induced superconductivity [2]. We also observed that substitution of divalent Sr$^{+2}$ for La$^{+3}$ (hole doping) does not induce superconductivity [2]. Electrical resistivity measurements were also performed under applied pressure on $Ln$O$_{0.5}$F$_{0.5}$BiS$_2$ ($Ln$ = La, Ce, Pr, Nd) up to $\sim$3 GPa and down to 1 K. These studies revealed a universal behavior where the systems are tuned away from semi-conducting behavior towards metallic behavior. The superconducting states were stabilized by applied pressure, so that $T_c$ ~increased in all of the rare earth members listed. At a critical pressure $P_c$, $T_c$ increases rapidly from a low $T_c$ phase to a distinct high $T_c$ phase, after which additional pressure no longer suppressed the semiconducting behavior in the normal state [3,4]. In addition, the metallization of NdO$_{0.5}$F$_{0.5}$BiS$_2$ also occurs at $P_c$.\\[4pt] This work was performed in collaboration with M. B. Maple, K. Huang, B. D. White and C. T. Wolowiec. \\[4pt] [1] Yazici et al, Philos. Mag. 93, 673, (2012).\\[0pt] [2] Yazici et al, Phys. Rev. \textbf{B} 87, 174512, (2013).\\[0pt] [3] Wolowiec et al, Phys. Rev. \textbf{B} 88, 064503, (2013).\\[0pt] [4] Wolowiec et al, Journal of Physics: Condensed Matter 25, 422201, (2013). [Preview Abstract] |
Tuesday, March 4, 2014 9:12AM - 9:24AM |
F52.00005: High Pressure Synthesis and properties of (Ca,Pr)Fe$_{2}$As$_{2}$ Tyler Drye, Valentin Taufour, Udhara Kaluarachchi, Sheng Ran, Paul Canfield, Johnpierre Paglione Despite impressively high superconducting transition temperatures approaching 50 K, superconductivity in rare earth-doped CaFe$_{2}$As$_{2}$ appears to only involve a small volume fraction as determined by shielding fraction. In addition, the amount of Pr that can be doped into the system via ambient pressure flux synthesis is limited to \textless 15{\%}, due to a width of formation limitation. We report a study using high-pressure flux growth to substitute higher levels of Pr approaching 40{\%} concentration. The superconducting properties of the resultant crystals are presented, including chemical composition, resistivity, and magnetization measurements. The final result is a complete phase diagram for the Pr-doped CaFe$_{2}$As$_{2}$ system. [Preview Abstract] |
Tuesday, March 4, 2014 9:24AM - 9:36AM |
F52.00006: Synthesis and characterization of single crystal of iso-valent doped K1-xNaxFe2As2 Yu Li, Chenglin Zhang, Pengcheng Dai KFe2As2 is a very special member of iron based superconductors and has attracted a lot of attention. With peculiar topology of Fermi surfaces and incommensurate spin fluctuation due to nesting between hole pockets and the electron-like band above Fermi level, different electron pairing symmetries were proposed. However, due to the limitation of single crystal size, there are not so many experiments (especially neutron scattering) on KFe2As2 systems. To solve this problem, we grow iso-valent doped K1-xNaxFe2As2. Big crystals are grown and they are much easier to handle than KFe2As2. By magnetic susceptibility and ICP measurements, we find a small doping dependent of Tc from 3.3K to 2.8K, confirming the chemical pressure effect of Sodium doping. Our neutron scattering data on nominal K0.5Na0.5Fe2As2 also shows identical incommensurate fluctuation discovered in KFe2As2, suggesting similar magnetic behavior between both of them. We will present some inelastic neutron scattering results on this system. [Preview Abstract] |
Tuesday, March 4, 2014 9:36AM - 9:48AM |
F52.00007: Correlation of superparamagnetism and self-assembled defects with non-bulk superconductivity up to 49 K in (Ca,Pr)Fe$_{2}$As$_{2}$ single crystal Bing Lv, F.Y. Wei, L.Z. Deng, Y.Y. Xue, C.W. Chu We have found the unusual simultaneous occurrence of superparamagnetism and superconductivity single crystals of (Ca$_{1-x}$Pr$_{x}$)Fe$_{2}$As$_{2}$ with an x-independent Tc and a close correlation of the superconducting volume fraction with the magnetic cluster density and self-assembled As-defect density. The finding demonstrates a close relationship of superconductivity with superparamagnetism associated with the self-assemble defects. In addition, we have detected extremely large magnetic anisotropy, doping level independent Tc, the existence of mesoscopic-2D structures and Josephson-Junction Array couplings in the system. All these observations provide the physical basis of interfaces for the proposed interface-mechanism, and the best evidence for interface-enhanced superconductivity in a naturally occurring (vs artificially synthesized) material system to date. [Preview Abstract] |
Tuesday, March 4, 2014 9:48AM - 10:00AM |
F52.00008: LaFe$_{0.6}$Sb$_{2}$: Strongly to weakly correlated system with Ni doping J.C. Misuraca, J.W. Simonson, J.J. Kistner-Morris, A. Puri, T. Orvis, L.H. Greene, M.C. Aronson Since the discovery of superconducting Ca$_{\mathrm{1-x}}$La$_{\mathrm{x}}$FeAs$_{2}$ with a T$_{\mathrm{c}}$ of 34 K [1], there has been an increasing interest in growing 112 iron pnictides in the search for high T$_{\mathrm{c}}$ superconductivity. We have grown large single crystals of LaFe$_{0.6}$Sb$_{2}$, which form in a tetragonal 112 structure with a significant amount of Fe vacancies, confirmed via single crystal x-ray diffraction. We present a doping study utilizing Ni which replaces both the Fe and vacancies while transforming the material from strongly to weakly correlated, as determined by low temperature heat capacity measurements. The Sommerfeld coefficient $\gamma $ of the undoped crystal is 50 mJ/mol Fe K$^{2}$, indicating a large mass enhancement, while LaNiSb$_{2}$ is 5 mJ/mol Ni K$^{2}$ with no vacancies and up to 18{\%} interstitial Ni according to energy-dispersive x-ray spectroscopy. When doping LaFeSb$_{2}$ with Ni, $\gamma $ remains constant when normalized per transition metal, possibly indicating a constant density of states. A divergence appears in C/T vs. T$^{2}$ once the vacancies are filled, at 89{\%} Ni, and the divergence remains until the LaNiSb$_{2}$ sample, which is a weakly correlated 1 K superconductor. [1] Katayama, et al. arXiv:1311.1303v1 (2013). [Preview Abstract] |
Tuesday, March 4, 2014 10:00AM - 10:12AM |
F52.00009: Interplay between magnetic impurity and superconductivity in annealed Fe1.05Te0.75Se0.25 Wenzhi Lin, Panchapakesan Ganesh, Anthony Gianfrancesco, Tom Berlijn, Thomas Maier, Sergei Kalilin, Brian Sales, Minghu Pan By annealing Fe1.05Te0.75Se0.25 in Te vapor, we are able to recover the moment of the magnetic impurity in the bulk chalcogenide superconductor, and enhance the superconductivity in the material. Scanning tunneling microscopy/ spectroscopy studies across a local magnetic impurity reveal the modification of electronic structure around the impurity on the surface of Fe1.05Te0.75Se0.25 sample after being annealed in the Te-vapor. The superconducting gap feature, normally seen on a pristine area, is suppressed around the magnetic impurity. In addition, density-functional theory calculations are carried out to identify the atomic structure, chemical composition and magnetic moment of impurity. \\ Research was supported (WL, BCS, SVK) by Materials Sciences and Engineering Division, Basic Energy Sciences, the U.S. Department of Energy. This research was conducted (WL, MP) at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Fellowship support (AG) from the UT/ORNL Bredesen Center for Interdisciplinary Research and Graduate Education. [Preview Abstract] |
Tuesday, March 4, 2014 10:12AM - 10:24AM |
F52.00010: Vortex Matter Studies in Iron Arsenide Sr$_{2}$O$_{3}$VO$_{3}$FeAs Oscar Ayala-Valenzuela, Man-Jin Eom, Jong-Mok Ok, Jun-Sung Kim, Han-Woong Yeom, Jeehoon Kim In a high temperature superconductor (HTSC), at finite temperatures, vortices jump from one pinning center to another in response to the driving force of the current. In several cases this flux creep in Fe-based is larger than in cuprates HTSC. Thermal fluctuations in HTSC also produce melting of the vortex lattice and the appearance of vortex liquid phases, characterized by $J_{c}=$0, near the critical temperature ($T_{c})$. In general, Fe-based superconductors also exhibit large vortex fluctuation effects, in spite of their lower T$_{c}$. Liquid phases are observed in many of these compounds; their extension and characteristics are topics of extensive current research. We have explored vortex fluctuation effects in a single-crystal of Sr$_{2}$VO$_{3}$FeAs by measuring magnetization and its time decay in a SQUID magnetometer. Despite the lower T$_{c}$ and small anisotropy, we found creep rates even higher than in other HTSC. We also observed wider liquid phases that covers most of the mixed state region in the H-T phase diagram. These unusually strong fluctuations are a consequence of the very large penetration depth $\lambda $, which results in Ginzburg numbers ($G_{i})$ higher than in cuprates. In the present study we use classical theories developed for cuprates, and compare them with other Fe-based superconductors. [Preview Abstract] |
Tuesday, March 4, 2014 10:24AM - 10:36AM |
F52.00011: Electron-doping-induced insulator-to-superconductor transition in a BiS$_{2}$-based superconductor Sr$_{1-x}$La$_{x}$FBiS$_{2}$ Hideaki Sakai, Daichi Kotajima, Kosuke Saito, Hiroki Wadati, Yuki Wakisaka, Masaichiro Mizumaki, Kiyofumi Nitta, Yoshinori Tokura, Shintaro Ishiwata Recently, materials with BiS$_{2}$ layers have attracted much attention as a new family of layered superconductors. Superconductivity was first reported in Bi$_{4}$S$_{4}$O$_{3}$, followed by $R$O$_{1-x}$F$_{x}$BiS$_{2}$, Sr$_{0.5}$La$_{0.5}$FBiS$_{2}$, and Bi$_{3}$O$_{2}$S$_{3}$. So far, however, comprehensive studies about the dependence on carrier concentration have been still lacking. In this study, we have systematically synthesized polycrystalline Sr$_{1-x}$La$_{x}$FBiS$_{2}$ ($0\!\le\! x\!\le\! 0.6$) to reveal the electronic phase diagram associated with the superconductivity in the BiS$_{2}$ layer. Since the density of states of the Sr, La and F orbitals is negligibly small near the Fermi level, this series of compounds would allow the rigid-band carrier doping and provide an ideal arena to study the detailed concentration dependence. The obtained phase diagram is characterized by an insulator-superconductor transition with a steep phase boundary at $x\!\sim\!0.4$. This is markedly different from that for $R$O$_{1-x}$F$_{x}$BiS$_{2}$, indicating a strong impact of the blocking layer on the superconductivity. Unusual increase in $T_{\rm c}$ has been also revealed as the carrier concentration decreases toward the critical point [1]. [1] H. Sakai {\it et al.} JPSJ (accepted) [Preview Abstract] |
Tuesday, March 4, 2014 10:36AM - 10:48AM |
F52.00012: ABSTRACT WITHDRAWN |
Tuesday, March 4, 2014 10:48AM - 11:00AM |
F52.00013: Copper Substituted Iron Telluride: A Phase Diagram Patrick Valdivia Investigations of superconductivity in the FeCh family (Ch$=$S,Se,Te) have produced rich physics and notable materials challenges despite the ostensible simplicity of thE system. We have studied the effects of copper substitution in iron-telluride. We map out basic physical parameters of this phase diagram and invesitgate structure-property relationships through a variety of transport and diffraction measurements. [Preview Abstract] |
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