Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Y5: Focus Session: Fe-based Superconductors -- Materials Synthesis and Charactarization |
Hide Abstracts |
Sponsoring Units: DMP DCOMP Chair: Athena Safa-Sefat, Oak Ridge National Laboratory Room: Juan Gorman Room 005 |
Friday, March 6, 2015 8:00AM - 8:12AM |
Y5.00001: Doping evolution of the anisotropic upper critical field in (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ Makariy Tanatar, Yong Liu, T.A. Lograsso, Ruslan Prozorov, Jan J. Jaroszynski, J.S. Brooks The temperature and magnetic field- dependent in-plane resistivity measurements were used to determine anisotropic upper critical field, $H_{c2}(T)$, of the hole-doped iron-based superconductor (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ over the whole doping range $x$=0 to $x$=1. We find clear saturation of $H_{c2}(T)$ line on $T \to 0$ in magnetic field perpendicular to the $c$-axis of the samples in the overdoped range of the phase diagram, suggesting strong paramagnetic limiting effects. Measurements reveal clear difference in the shapes of the $H_{c2}(T)$ lines for under-doped and over-doped compositions with similar $T_c$. Origin of this difference will be discussed. [Preview Abstract] |
(Author Not Attending)
|
Y5.00002: Investigation of Vortex Lattice in Optimally Doped (Ba$_{1-x}$K$_{x}$)Fe$_{2}$As$_{2}$ Using SANS S. Demirdis, C.J. van der Beek, S. Muhlbauer, Y. Su, Th. Wolf Small-angle neutron scattering is used to study the vortex lattice (VL) in optimally doped (Ba1-xKx)Fe2As2 single crystal. Previous SANS studies, as well as real-space imaging methods applied to the study of the VL in single crystalline (Ba1-xKx)Fe2As2, Co-, and P-substituted BaFe2As2, have consistently reported highly disordered vortex structures. Present SANS study reveals the first time in doped pnictides, clear vortex lattice Bragg peaks. Here we show SANS data taken in a magnetic field ranging between 0.25 and 2 Tesla that reveals resolution limited sharp Bragg spots, indicating the existence of a long-range ordered Bragg glass. Field dependence of the vortex structure factor, obtained by correcting the intensity by the field-dependent vortex form factor, shows a sharp drop well below the second critical field. This vortex structural transition shows clear correlations with features observed around the so-called ``second magnetization peak'' present in isothermal hysteresis loops. [Preview Abstract] |
Friday, March 6, 2015 8:24AM - 8:36AM |
Y5.00003: Metallic insulator transition in K-doped BaMn$_{2}$As$_{2}$: Magnetic, optical, and transport properties of BaMn$_{2}$As$_{2}$ and Ba$_{\mathrm{1-x}}$K$_{\mathrm{x}}$Mn$_{2}$As$_{2}$ Shelby Zellman, Daniel McNally, Kangbo Hao, Kirk Post, Dimitri Basov, Christopher Homes, Meigan Aronson Square-net Mn- pnictides are strongly correlated antiferromagnetic (AF) insulators that can potentially be transformed into metals using pressure or charge doping. BaMn$_{2}$As$_{2}$ becomes an AF metal when 5{\%} of K is substituted on the Ba site, and we present here an optical study of this insulator-metal transition. Our measurements confirmed that the resistivity r(T) of undoped BaMn$_{2}$As$_{2}$ is insulating, but becomes metallic with as little as 5{\%}K doping. We measured optical transmission in the visible region of BaMn$_{2}$As$_{2}$, finding a direct charge gap of $\sim$ 5500 cm$^{-1}$, much larger than previously reported, or the activation gaps determined from r(T). Reflectance measurements were performed to determine if a Drude peak forms at the lowest energies in the doped samples. These measurements underscore the importance of electron correlations in BaMn$_{2}$As$_{2}$ as it approaches metallization. We acknowledge the Office of the Assistant Secretary of Defense for Research and Engineering for providing the NSSEFF funds that supported this research and the DOE under contract No. DE-AC02-98CH10886. [Preview Abstract] |
Friday, March 6, 2015 8:36AM - 8:48AM |
Y5.00004: The Ni and Co substitutions in iron chalcogenide single crystals V.L. Bezusyy, D.J. Gawryluk, A. Malinowski, M. Berkowski, Marta Z. Cieplak We study the \textit{ab}-plane resistivity and Hall effect in Fe$_{\mathrm{1-y}}$M$_{\mathrm{y}}$Te$_{\mathrm{0.65}}$Se$_{\mathrm{0.35}}$ single crystals with M$=$Co or Ni, and y up to 0.2. The crystals are grown by Bridgman's method. The low-temperature Hall coefficient R$_{\mathrm{H}}$ changes sign to negative for crystals with y exceeding 0.135 (Co) and 0.06 (Ni), consistent with the electron doping induced by these impurities. However, the R$_{\mathrm{H}}$ remains positive for all samples at high T, suggesting that remnant hole pockets survive the doping, but the holes become localized at low T in heavily doped crystals. Superconducting transition temperature (Tc) approaches zero for y $=$ 0.14 (Co), and 0.03 (Ni), while the resistivity at the Tc onset is only weakly affected by Co doping, but it increases strongly for the Ni. These results suggest that in case of Co impurity the Tc suppression may be attributed to electron doping. On the other hand, the Ni substitution, in addition to electron doping, induces strong localization effects at small impurity contents. Using two-band conduction model we argue that the localization of electron carriers is responsible for strong superconductivity suppression by Ni impurity. [Preview Abstract] |
Friday, March 6, 2015 8:48AM - 9:00AM |
Y5.00005: Generic Superconducting Inhomogeneity in Single Crystal Fe(Te$_{1-x}$Se$_{x})$ Probed by Nanostructure-transport Chunlei Yue, Jin Hu, Xue Liu, Zhiqiang Mao, Jiang Wei We have investigated the nano-scale electronic properties of the iron-based unconventional superconductor Fe(Te$_{1-x}$Se$_{x})$ with optimal Se content $x=$0.5. Using the microexfoliation method and ion milling thinning, we successfully produced Fe(Te$_{1-x}$Se$_{x})$ devices with thickness varying from 90nm down to 12nm. Our transport measurements revealed a suppression of superconductivity coinciding with the loss of normal state metallicity. Through the simulation of the formation of superconducting region in nano-scale thin flakes, we show that our observation is in line with the nano-scale inhomogeneity proposed for this material; therefore it provides a more direct evidence for the nano-scale inhomogeneous superconductivity in Fe(Te$_{1-x}$Se$_{x})$. [Preview Abstract] |
Friday, March 6, 2015 9:00AM - 9:36AM |
Y5.00006: Order/disorder of Fe-vacancy and superconductivity in Fe-chalcogenide superconductors Invited Speaker: Maw-Kuen Wu Having the simplest crystal structure among the Fe-based superconductors, the FeSe superconductor is the best candidate for investigating the mechanism of these new superconductors. How the properties of FeSe superconductor evolve from normal state to superconducting state and what is the parent phase of FeSe system are critical issues for resolving its superconducting mechanism. We have studied the properties of FeSe and K-Fe-Se superconductors in various forms, including polycrystal, single crystal, thin film, nanowire, and nanoparticle. We discovered several Fe-deficient Fe1-xSex phases, which exhibit Fe-vacancy ordering. The property of these phases evolves from an insulator to a metal gradually as Fe content increases. Our results provide unambiguous support to the picture that superconducting transition in FeSe and related compounds is closely related to the order to disorder transition of the Fe-vacancy. [Preview Abstract] |
Friday, March 6, 2015 9:36AM - 9:48AM |
Y5.00007: Fermi-liquid like normal state electrodynamics in Co-doped BaFe$_2$As$_2$ Erik Van Heumen, Alona Tytarenko, Yingkai Huang, Anne de Visser, Steven Johnston Elucidating the origin of high temperature superconductivity requires two equally important ingredients: a framework for the normal state electron dynamics and a pairing interaction. In iron-pnictide high T$_{c}$ superconductors the electron doped compounds, such as BaFe$_{2-x}$Co$_{x}$As$_{2}$, are predicted to be weakly correlated Fermi liquids [1,2], but clear evidence has thus far been lacking. In this contribution we unveil the true nature of the normal state dynamics by carefully annealing BaFe$_{1.8}$Co$_{0.2}$As$_{2}$ single crystals. We show that optical spectroscopy experiments on such annealed crystals display a characteristic Fermi liquid scaling of frequency and temperature over a large energy range [3]. A comparison with as-grown single crystals shows that magnetic impurity scattering has thus far masked this behavior. A further analysis shows that a Fermi-liquid like single-particle self-energy can well describe both the mass renormalization and optical scattering rate, leaving little room for additional contributions.\\[4pt] [1] P. Werner et al., Nature Phys. 8, 1 (2012).\\[0pt] [2] L. De' Medici et al., Phys. Rev. B 83, 205112 (2011).\\[0pt] [3] C. Berthod et al., Phys. Rev. B 87, 115109 (2013). [Preview Abstract] |
Friday, March 6, 2015 9:48AM - 10:00AM |
Y5.00008: Anomalous Hall effect in epitaxial Ba(Fe1-x Cox)2As2 pnictide superconducting thin films and superlattices Neil Campbell, Mark Rzchowski, Julian Irwin, Jong-Hoon Kang, Chang-Beom Eom, Sanghan Lee, Adele Ruosi Iron-based superconductors have been worked with to the point that now growth of various thin films is very-well controlled, allowing in depth study of associated structures. One exciting pathway of study for pnictides is that they show similarities to cuprate superconductors, regarded as an avenue toward high-Tc superconductors. Specifically, these heterostructures allow study of the competition between antiferromagnetism and superconductivity at the interface between the undoped parent compound, and optimally-doped compound, BaFe2-xCoxAs2 (Ba122). At room temperature, these pnictides exhibit anomalous Hall effect (AHE). There is strong evidence for the interface dominating AHE, allowing control AHE with type of substrate, surface termination, and superlattice configuration. We characterized samples of thicknesses from 6nm to 300nm, and with up to 12 interfaces. Such samples have been characterized via magnetotransport measurements at temperatures ranging from 5K to 300K, and magnetic fields up to 8T applied normal to the basal plane with Van der Pauw and Hall geometries. Additionally, we measured magnetization with vibrating sample magnetometry. These properties will aid novel device development, making pnictides interesting. [Preview Abstract] |
Friday, March 6, 2015 10:00AM - 10:12AM |
Y5.00009: Electrodynamics of rare-earth-doped CaFe$_{2}$As$_{2}$ Zhen Xing, T.J. Huffman, Peng Xu, A.J. Hollingshad, D.J. Brooker, M.M. Qazilbash, Shanta Saha, Tyler Drye, Connor Roncaioli, J. Paglione Rare-earth substitution at alkaline-earth sites leads to the suppression of the spin density wave phase transition in CaFe$_{2}$As$_{2}$ without the emergence of bulk superconductivity. In this work, we perform cryogenic infrared reflectance spectroscopy and spectroscopic ellipsometry on Pr-doped and La-doped CaFe$_{2}$As$_{2}$ single crystals. In both Ca$_{0.8}$La$_{0.2}$Fe$_{2}$As$_{2}$ and Ca$_{0.85}$Pr$_{0.15}$Fe$_{2}$As$_{2}$ samples, the spin density wave transition is completely suppressed. The temperature dependence of the \textit{ab}-plane optical conductivity of the La-doped CaFe$_{2}$As$_{2}$ crystal exhibits conventional metallic behavior consistent with the absence of any structural, magnetic, or superconducting instabilities. On the other hand, the Pr-doped CaFe$_{2}$As$_{2}$ crystal undergoes a structural transition about 70 K from a tetragonal lattice to a collapsed tetragonal lattice with the same symmetry but reduced volume. In the Pr-doped CaFe$_{2}$As$_{2}$ crystal, the \textit{ab}-plane optical conductivity reveals subtle but distinct spectral changes upon cooling through the structural transition. We provide results on the influence of the structural collapse on the charge dynamics, correlation effects and the electronic configuration. [Preview Abstract] |
Friday, March 6, 2015 10:12AM - 10:24AM |
Y5.00010: Systematic growth and physical properties of BaFe$_{2-x-y}$Cr$_{y}$Ni$_{x}$As$_{2}$ Dongliang Gong, Rui Zhang, Shiliang Li, Pengcheng Dai, Huiqian Luo We have successfully grown the single crystals of BaFe$_{2-x-y}$Cr$_{y}$Ni$_{x}$As$_{2}$ with a series of Ni and Cr doping levels. Their physical properties were studied by the elastic neutron scattering and transport measurements. It is found that Cr doping is a very efficient way of suppressing the superconductivity in the BaFe$_{2-x}$Ni$_{x}$As$_{2}$ system with little change of the T$_{S}$ and T$_{N}$. The magnetic and electronic properties without the presence of the superconductivity may be thus investigated at low temperature. [Preview Abstract] |
Friday, March 6, 2015 10:24AM - 10:36AM |
Y5.00011: Observation of pseudogaplike feature in LiFeAs by ultrafast optical spectroscopy Kung-Hsuan Lin, Kuan-Jen Wang, Chung-Chieh Chang, Yu-Chieh Wen, Dzung-Han Tsai, Yu-Ruei Wu, Yao-Tsung Hsieh, Ming-Jye Wang, Bing Lv, Paul C.-W. Chu, Mau-Kuen Wu We utilize ultrafast optical spectroscopy to study the quasiparticle relaxation in stoichiometric LiFeAs crystals. According to our temperature-dependent studies, we have observed three electronic phases in LiFeAs. Below the superconducting (SC) temperature Tc ($=$ 15 K), the relaxation time of quasiparticles due to the SC gaps is far longer than 50 ps in our experimental conditions. In addition to SC gaps, we have also found a gaplike feature in SC state. This gaplike feature is evident up to 40 K, which is above the SC temperature. Because this is similar to pseudogap in curate superconductors, we call this new electronic phase as pseudogaplike feature. The quasiparticle relaxation time due to pseudogaplike feature is in the range of 1-2 ps. We suggest the pseudogaplike feature in LiFeAs is induced by magnetic fluctuations. [Preview Abstract] |
Friday, March 6, 2015 10:36AM - 10:48AM |
Y5.00012: Temperature Evolution of Spin Fluctuations in FeAs A. Podlesnyak, G. Ehlers, S. T\'{o}th, K. Gofryk, A.S. Sefat The discovery of superconductivity (SC) in iron pnictides has opened a new stage in SC research. The superconducting state appears in iron pnictides with doping in metallic parent compounds. This is an important difference to the cuprates, which exhibit SC near a correlated insulating state. Therefore, the nature of the magnetism in the simplest iron pnictide - binary FeAs - is of fundamental importance for understanding the interplay between localized and itinerant magnetism and superconductivity in these materials. We use inelastic neutron scattering to map spin wave excitations in the monoarsenide FeAs at temperatures above and below the antiferromagnetic transition T$_{\mathrm{N}}$ $\sim$ 70 K. We find magnetic excitation spectrum near the N\'{e}el temperature to be strongly different from the spectrum in the ground state. Near the transition temperature, magnetic fluctuations clearly indicate two-dimensional character in an intrinsically three-dimensional (3D) system. On the other hand, at low temperature, spin waves in FeAs are anisotropic 3D, suggesting a crossover from two-dimensional to three-dimensional character. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700