Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session B13: Focus Session: Fe-Based Superconductors-1111's,122's |
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Sponsoring Units: DMP Chair: Athena Sefat, Oak Ridge National Laboratory Room: 207 |
Monday, March 3, 2014 11:15AM - 11:51AM |
B13.00001: A Study of Hydrogen Anion Substitution in 1111-type Iron Arsenides Invited Speaker: Hideo Hosono Hydrogen is the simplest bipolar element and its valence state can be controlled from $+$1 to $-$1. We have synthesized the 1111-type iron arsenides CaFeAsH and LnFeAsO1$-$xHx (Ln $=$ lanthanide; 0 $\le $ x $\le $ 0.5) with the ZrCuSiAs type structure by a high-pressure synthesis method. The position and valence state of the substituted H were determined by neutron diffraction and density functional theory calculations. The close similarity in the structural and electrical properties of CaFeAsH and CaFeAsF indicated the formation of the hydride ion (H$-)$, which is isovalent with the fluoride ion (F$-)$, in the 1111-type iron arsenides. When some of the O2$-$ ions in LnFeAsO are replaced by H$-$, superconductivity is induced by electron doping to the FeAs-layer to maintain charge neutrality. Since the substitution limit of hydrogen in LnFeAsO (x $\approx $ 0.5) is much higher than that of fluorine (x $\approx $ 0.2), the hydrogen substitution technique provides an effective pathway for high-density electron-doping, making it possible to draw the complete electronic phase diagram of LnFeAsO. The x-T diagrams of LnFeAsO$_{1-x}$H$_x$ (Ln $=$ La, Ce, Sm, Gd) have a wide superconducting (SC) region spanning the range x $=$ 0.04 to 0.4, which is far from the parent antiferromagnetic region near x $=$ 0.0. For LaFeAsO$_{1-x}$H$_x$, another SC dome region was found in the range x $=$ $\sim$ 0.2 to $\sim$ 0.5 with a maximum Tc $=$ 36 K, in addition to a conventional SC dome located at x $\sim$ 0.08 with maximum Tc $=$ 29 K. Density functional theory calculations performed for LaFeAsO$_{1-x}$H$_x$ using virtual crystal approximation indicated that the newly observed Tc is correlated with the appearance of degeneration of the Fe 3d bands (dxy, dyz and dzx), which is caused not only by regularization of the tetrahedral shape of FeAs$_4$ due to chemical pressure effects but also by selective band occupation with doped electrons. Very recently, a new AFM phase was found around x$=$0.5, suggesting that the double dome Tc structure reflects the presence of two AFM phases at x$=$0 and 0,5. In this talk, I review the recent progress in superconductivity in 1111-type iron (oxy)arsenides and related compounds induced by hydrogen anion substitution. [Preview Abstract] |
Monday, March 3, 2014 11:51AM - 12:03PM |
B13.00002: Orbital Fluctuation Theory for LaFeAsO$_{1-x}$H$_x$: Pnictogen Height Instability and Superconductivity due to Orbital Fluctuations Youichi Yamakawa, Seiichiro Onari, Hiroshi Kontani The isostructural transition in the tetragonal ($C_4$) phase, with sizable change in the As-height, is realized in heavily H-doped LaFeAsO, Pr-doped CaFe$_2$As$_2$, and Na-doped BaFe$_2$As$_2$. Here, we study the mechanism of spin-fluctuation-driven structure transition in LaFeAsO$_{1-x}$H$_x$ by using the self-consistent vertex correction (SC-VC) method. In heavily-doped case ($x\sim0.5$), the non-nematic orbital order is caused by the VC due to $d_{xy}$-orbital spin fluctuations, and triggers the $C_4$ isostructural transition. In lightly-doped case ($x\sim0$), the orthorhombic phase is realized by the orbital-nematic order, which originates from the VC due to ($d_{xz},d_{yz}$)-orbital spin fluctuations. Both nematic and non-nematic orbital fluctuations contribute in realizing higher-$T_{\rm c}$ superconductivity. [Preview Abstract] |
Monday, March 3, 2014 12:03PM - 12:15PM |
B13.00003: Transport properties of LaFeP$_{1-x}$As$_{x}$O$_{1-y}$F$_{y}$: Evidence for two superconducting states Kwing To Lai, Akira Takemori, Shigeki Miyasaka, Setsuko Tajima Resistivity and Hall coefficient of polycrystalline LaFeP$_{1-x}$As$_{x}$O$_{1-y}$F$_{y}$ with $x$ = 0 -- 1.0 and $y$ = 0 -- 0.1 have been investigated. In the $T_{c}$-$x$ phase diagram for F-free ($y$ = 0) samples, two superconducting domes have been revealed at $x$ = 0 -- 0.3 ($T_{c}^{max}$ $\sim $12 K) and 0.6 -- 0.8 ($T_{c}^{max}$ $\sim $10 K). Hall effect measurements suggest that the electronic states in these two dome regions are different from each other. For $y$ = 0.05, double peaks of $T_{c}$ are observed at $x$ $\sim $ 0.4 and 0.8, while only one dome with $T_{c}^{max}$ $\sim$28 K is observed for $y$ = 0.1 [1]. These changes can be regarded as the fusion of two $T_{c}$ domes upon F doping. \\[4pt] [1] S. Miyasaka et al., to be published in J. Phys. Soc. Jpn. (arXiv:1310.2731). [Preview Abstract] |
Monday, March 3, 2014 12:15PM - 12:27PM |
B13.00004: Comparison of specific heat and magneto-resistance measurements in the same SmFeAsO$_{1-x}$F$_{x}$ crystals Stanislaw Galeski, Philip Moll, Nikolai Zhigadlo, Janusz Karpinski, Bertram Batlogg We have performed resistivity and specific heat measurements in the same sub-microgram single crystals of an iron-based superconductor SmFeAsO1-xFx (T$_{c} \approx $ 50K). This allowed for the first direct comparison of Hc2 curves from thermodynamic measurements with estimates from the magneto-resistance at commonly used criteria (10, 50, 90{\%} $\varrho _{N})$. A criterion of 40-50{\%} $\varrho_{N}$ well describes H$_{c2}$(T) for both in and out of plane fields. We attribute the low field dependence of the criterion to filamentary superconductivity. The challenging heat capacity measurement on microscopic crystals (50$\mu$m in diameter, 10$\mu$m thick) was done using a commercially available gas-nanocalorimeter. The thermodynamic data was in good agreement with previous experiments performed on crystals from the same batch by other groups. H$_{c2}$ slopes of 1.6 T/K for fields parallel to the c-axis and 12.3 T/K in the ab-plane were found yielding a $\xi $ anisotropy $\gamma \approx $ 7. This demonstrates that our experimental technique is both relatively fast to set up and furthermore reliable in fields up to 6T. [Preview Abstract] |
Monday, March 3, 2014 12:27PM - 12:39PM |
B13.00005: Effect of nematic order on the spin fluctuation spectrum of LaFeAsO Qiang Zhang, Rafael M. Fernandes, Jiaqiang Yan, R.W. McCallum, Thomas A. Lograsso, Songxue Chi, David Vaknin, Robert J. McQueeney Inelastic neutron scattering measurements on the LaFeAsO antiferromagnetic (AFM) system reveal distinct temperature-dependent behavior in the low-energy spin dynamics. As expected, the dynamic susceptibility at the AFM wavevector peaks at the AFM transition temperature $T_{\mathrm{N}}$, but also displays an anomaly at the orthorhombic-to-tetragonal transition temperature $T_{\mathrm{S}}$. The spin-spin correlation length increases rapidly below $T_{\mathrm{S}}$ once long-range nematic order sets in. The sharp changes in both the dynamic susceptibility and the spin-spin correlation length at $T_{\mathrm{S}}$ evidence a strong effect of nematic order on the magnetic spectrum, in agreement with models that attribute the structural transition to an electronic nematic phase driven by spin fluctuations. [Preview Abstract] |
Monday, March 3, 2014 12:39PM - 12:51PM |
B13.00006: Temperature and composition dependence of the magnetically ordered, tetragonal C$_4$ phase in Ba$_{1-x}$Na$_x$Fe$_2$As$_2$ via neutron scattering Jared Allred, Daniel Bugaris, Omar Chmaissem, Stephan Rosenkranz, Sevda Avci, Pascal Manuel, Dmitry Khalyavin, Aziz Daoud-Aladine, Duck Young Chung, Helmut Claus, Mercouri Kanatzidis, Ray Osborn Until recently, the relationship between orthorhombic/magnetic order and superconductivity was believed well established in the 122 iron arsenide family. This changed when recent observations in the hole doped 122's: Ba$_{1-x}$K$_x$Fe$_2$As$_2$ ($0.16 \leq x \leq 0.21$) under pressure and Ba$_{0.76}$Na$_{0.24}$Fe$_2$As$_2$ at ambient pressure exhibit evidence of a new electronic phase being stabilized near the end of the magnetic dome, beginning at higher compositions than the onset of superconductivity . Using combined high-intensity and high-resolution neutron diffraction we have expanded the Na region to multiple compositions $0.24\leq x\leq 0.28$ all stabilized at ambient pressure. The magnetic and structural properties both differ from the paramagnetic tetragonal phase and the antiferromagnetic orthorhombic phase. The complex relationship between structure, magnetism, and superconductivity in this regime give important insights into the underlying physics. [Preview Abstract] |
Monday, March 3, 2014 12:51PM - 1:03PM |
B13.00007: Phase diagrams of K- and Na - doped BaFe$_2$As$_2$ as probed by heat capacity and hydrostatic pressure S.L. Bud'ko, D.Y. Chung, M. Sturza, D. Bugaris, M.G. Kanatzidis, P.C. Canfield Many iron-arsenide based superconductors present a simple scaling of the jump in specific heat at superconducting transition temperature $T_c$ with the value of $T_c$, $\Delta C_p \propto T_c^3$ (so called BNC scaling). A comprehensive study of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ over the whole range of K - concentrations showed clear deviation from the BNC scaling for $x > 0.7$. At the same concentrations anomalous behavior was observed in NMR and thermal conductivity measurements. This observation suggests change of the superconducting state for $x > 0.7$. The pressure dependence of $T_c$ (up to $\sim 1$ GPa) is linear or close to linear for all measured K-concentrations In contrast, the data for the large portion of Ba$_{1-x}$Na$_x$Fe$_2$As$_2$ ($0.2 \leq x \leq 0.9$) series follow the BNC scaling. In addition, the pressure dependence of $T_c$ (measured up to $\sim 1$ GPa) have clear non-linearities for Na concentration in 0.2-0.25 region, that may be consistent with an emergent, narrow, tetragonal $C4$ phase.\footnote{S. Avci et al., PRB 88, 094510 (2013).} [Preview Abstract] |
Monday, March 3, 2014 1:03PM - 1:15PM |
B13.00008: Disorder effects in multiorbital $s_{\pm}$-wave superconductors: Implications for Zn-doped BaFe$_2$As$_2$ compounds Hua Chen, Yuan-Yen Tai, C.S. Ting, Matthias J. Graf, Jianhui Dai, Jian-Xin Zhu Recent experiments on Zn-doped 122-type iron pnictides, Ba(Fe$_{1-x-y}$Co$_y$Zn$_x$)$_2$As$_2$, are challenging our understanding of electron doping the 122s and the interplay between doping and impurity scattering. To resolve this enigma, we investigate the disorder effects of nonmagnetic Zn impurities on various properties of the system in the $s_{\pm}$-wave pairing state. The BdG is solved based on a minimal two-orbital model with an extended range of impurity concentrations. With increasing Zn concentration the density of states shows a gradual filling of the gap, revealing pair breaking effect. Both the averaged superconducting order parameter and superfluid density are dramatically suppressed towards the dirty limit, indicating the violation of the Anderson theorem and breakdown of the AG theory for impurity-averaged Green's functions. The superconductivity is fully suppressed close to the critical impurity concentration of $n_{\mathrm{imp}}\approx 10\%$, in agreement with recent experiments. [Preview Abstract] |
Monday, March 3, 2014 1:15PM - 1:27PM |
B13.00009: Study on possible correlation of superconductivity with defects and superparamagnetism in undoped AFe$_{2}$As$_{2}$ with A$=$Ca, Sr and Ba Kui Zhao, Bing Lv, Liangzi Deng, Yuyi Xue, Paul Chu Extensive studies have been carried out on the induction of bulk superconductivity in the Fe-pnictide 122 system with a T$_{\mathrm{c}}$ up to 38 K through doping and/or pressure. However, non-bulk superconductivity has also been detected unexpectedly in undoped AFe$_{2}$As$_{2}$ where A $=$ Ca, Sr, and Ba with T$_{\mathrm{c}} =$ $\sim$12K, $\sim$22K and $\sim$23K, respectively. The reason for the observation remains unknown. Recently, systematic investigation shows that highly anisotropic superconductivity with a T$_{\mathrm{c}}$ up to 49 K and superparamagnetism occur in rare-earth doped Ca122. Further examination reveals slight deviation from the 1:2:2 stoichiometry which correlates closely with the occurrence of non-bulk superconductivity and superparamagnetism in these samples. We have therefore decided to investigate systematically the stoichiometry, defects, magnetism and superconductivity in undoped AFe$_{2}$As$_{2}$ single crystals under different synthesis conditions where A $=$ Ca, Sr, and Ba. Results will be presented and discussed. [Preview Abstract] |
Monday, March 3, 2014 1:27PM - 1:39PM |
B13.00010: Anisotropy reversal of in-plane resistivity in hole doped Ba(Fe$_{1-x}$TM$_x$)$_2$As$_2$ (TM=Mn, Cr) Tatsuya Kobayashi, Takumi Yamada, Kiyohisa Tanaka, Shigeki Miyasaka, Setsuko Tajima We investigated the in-plane anisotropy of resistivity across the magneto-structural transition in hole doped Ba(Fe$_{1-x}$TM$_x$)$_2$As$_2$ (TM=Mn, Cr) with detwinned single crystals. When the Mn and Cr-doping levels were low, the resistivity along the a-axis with antiferromagnetic spin alignment was smaller than that along the b-axis with ferromagnetic spin alignment, which is similar to that of electron doped BaFe$_2$As$_2$ [1]. However when x exceeds 0.09 in Cr-doped case, we observed the opposite resistivity anisotropy like that of (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ [2]. We will discuss the origin of the anisotropic resistivity and the difference between the effect of Cr and K doping. \\[4pt] [1] J. H. Chu et al., Science 329, 824 (2010)\\[0pt] [2] E. C. Blomberg et al., Nat. Commun. 4, 1914 (2013) [Preview Abstract] |
Monday, March 3, 2014 1:39PM - 1:51PM |
B13.00011: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 1:51PM - 2:03PM |
B13.00012: Emergence of high mobility hole-like carrier in Ba(Fe$_{\mathrm{1-x}}$Mn$_{\mathrm{x}}$As)$_{2}$ Yoichi Tanabe, Takahiro Urata, Khuong Huynh, Satoshi Heguri, Hidetoshi Oguro, Kazuo Watanabe, Katsumi Tanigaki An evolution of electronic states through impurity substitutions is one of key issues for understanding the electronic ground state of iron pnictides. In this talk, we will report the emergence of the hole-like carrier with high mobility in Ba(Fe$_{\mathrm{1-x}}$Mn$_{\mathrm{x}}$As)$_{2}$. A clear sign change of the Hall resistivity at low magnetic fields indicated that the electron-like high mobility carrier changes to the hole-like one through Mn substitution [1], although the nuclear magnetic resonance revealed that the Mn substitution does not introduce any carrier doping [2]. The evolution of p-type carrier will be discussed based on results of conductive tensor analyses. \\[4pt] [1] T. Urata et al., arxiv1307.2813.\\[0pt] [2] Y. Texier et al., EPL, 99, 17002 (2012). [Preview Abstract] |
Monday, March 3, 2014 2:03PM - 2:15PM |
B13.00013: Iron-based superconductors under heavy compression after destruction of superconductivity Xiaojia Chen, Yong-Hui Zhou, Jian-Jun Ying, Takaki Muramatsu, Viktor Struzhkin, Ho-Kwang Mao, Zhu-An Xu, Xian-Hui Chen, Guang-Yong Xu, Gen-Da Gu Choosing electron and hole doped Ba$_{1-y}$K$_{y}$Fe$_{2-x}$A$_{x}$As$_{2}$ (A=Ni,Co) and Fe$_{1+y}$Se$_{1-x}$Te$_{x}$ -- typical iron pnictides and chalcogenides, we investigate pressure effects on the physical properties of these superconductors after their superconductivity is completely destroyed. Combining electrical resistance and magnetic susceptibility measurements at pressures above 60 GPa, we establish extended pressure - temperature phase diagrams for these compounds. Contrary to the general belief of the existence of Fermi liquid after the disappearance of superconductivity upon compression, we find an unexpected insulating state in these heavily compressed compounds. Some novel behaviors such as reentrance of superconductivity are also discovered. These results indicate that rich physics is still hidden in iron-based superconductors. [Preview Abstract] |
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