Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session A39: Focus Session: Iron Superconductors: New Materials |
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Sponsoring Units: DMP DCMP Chair: Athena Sefat, Oak Ridge National Laboratory Room: F150 |
Monday, March 15, 2010 8:00AM - 8:36AM |
A39.00001: Crystal chemical aspects of superconductivity in BaFe$_{2}$As$_{2}$ and related compounds Invited Speaker: BaFe$_{2}$As$_{2}$ is the parent compound of the 122-type iron arsenides.$^{1}$ Superconductivity can be induced by several kinds of doping$^{2-4}$ or by pressure.$^{5}$ It is widely accepted that superconductivity in iron arsenides is unconventional and a number of experiments agree with the s$\pm $-scenario.$^{6}$ The latter relies on Fermi surface nesting which depends on both the electron count and the lattice. However, the coincidence of doping and pressure effects on the structure of BaFe$_{2}$As$_{2}$ supports the role of the structure.$^{7}$ Another open issue is the co-existence of superconductivity and AF magnetic ordering. Our $^{57}$Fe-M\"{o}ssbauer experiments with underdoped Ba$_{0.8}$K$_{0.2}$Fe$_{2}$As$_{2}$ ($T_{c}$ = 24 K) revealed full magnetic splitting, which indicates such a co-existence.$^{8}$ Compounds like Sr$_{2}$VO$_{3}$FeAs ($T_{c}$ = 37-45 K) are promising candidates for higher $T_{c}$, but their crystal chemistry is not yet understood. In non-superconducting Sr$_{2}$CrO$_{3}$FeAs, we have detected a non-stoichiometry of the Fe-site (Fe$_{0.93(1)}$Cr$_{0.07(1)})$ and $C$-type AF ordering of the Cr$^{3+}$-layers.$^{9}$ The Cr-doping of the FeAs layer is probably detrimental to superconductivity in Sr$_{2}$CrO$_{3}$FeAs, but a similar non-stoichiometry may play a vital role in Sr$_{2}$VO$_{3}$FeAs.\\ -\\ $^{1 }$M. Rotter, M. Tegel, I. Schellenberg, et al., Phys. Rev. B \textbf{78}, 020503 (2008).\\ $^{2 }$M. Rotter, M. Tegel, and D. Johrendt, Phys. Rev. Lett. \textbf{101}, 107006 (2008).\\ $^{3 }$S. Jiang, C. Wang, Z. Ren, et al., J. Phys.: Condens. Matter \textbf{21}, 382203 (2009).\\ $^{4 }$A. S. Sefat, R. Jin, M. A. McGuire, et al., Phys. Rev. Lett. \textbf{101}, 117004 (2008).\\ $^{5 }$P. L. Alireza, Y. T. C. Ko, J. Gillett, et al., J. Phys.: Condens. Matter \textbf{21}, 012208 (2009).\\ $^{6 }$I. Mazin, D. J. Singh, M. D. Johannes, et al., Phys. Rev. Lett. \textbf{101}, 057003 (2008).\\ $^{7 }$M. Rotter, M. Pangerl, M. Tegel, et al., Angew. Chem. Int. Ed. \textbf{47}, 7949 (2008).\\ $^{8 }$M. Rotter, M. Tegel, I. Schellenberg, et al., New J. Phys. \textbf{11}, 025014 (2009).\\ $^{9 }$M. Tegel, Y. Su, F. Hummel, et al., arXiv0911.0450. [Preview Abstract] |
Monday, March 15, 2010 8:36AM - 8:48AM |
A39.00002: New iron pnictide oxide with thick perovskite-type blocking layers Hiraku Ogino, Shinya Sato, Yutaka Matsumura, Naoto Kawaguchi, Kenji Machida, Yasuaki Shimizu, Koichi Ushiyama, Shigeru Horii, Jun-ichi Shimoyama, Kohji Kishio Since the discovery of high-Tc superconductivity in LaFeAs(O,F), development of the materials having iron or nickel pnictide layers are subject of study. As presented in last APS March meeting, we have discovered iron and nickel pnictide oxide superconductors with perovskite-type oxide layers[1]. Until now, several compounds of this system have been found such as (M'2Pn2)(Sr4M2O6) [M' = Fe, Ni; Pn = P, As; M = Sc, Cr, (Mg,Ti)]. These compounds have higher pnictogen heights and lower Pn-Fe-Pn angles compared to REFeAsO system. These features of the system may lead to realization of high-Tc superconductivity. Recently we discovered new material belongs to this kind of system. Structural features and physical properties of the compounds in this system as well as new compound will be presented. [1] H. Ogino et al., Supercond. Sci. Technol. 22 (2009) 075008. [Preview Abstract] |
Monday, March 15, 2010 8:48AM - 9:00AM |
A39.00003: Ab Initio Calculations on Magnetic, Electronical and Lattice Dynamical Properties of superconductor CeFeAsO Cihan Parlak, Resul Eryigit Recent reports of superconductivity in LaFeAsO has led to considerable interest as this provides an alternative noncuprate route to high $Tc$ superconductivity with possibly different superconductivity mechanism. After LaFeAsO, other members of the Fe-As oxypnictides family have been investigated and found to be superconducting. We have investigated the properties of CeFeAsO by using first-principles calculations. The calculations have been carried out within the local density functional approximation (LDA) using norm-conserving pseudopotentials and a plane-wave basis. Energetically favored magnetic structure is found to be a striped AFM Fe layer and zigzaged Ce layers with magnetic moments of 2.7 $\mu_B$ and 0.8 $\mu_B$ respectively. U parameters are estimated to be 3.62 eV and 4.51 eV for Fe and Ce, respectively. We discuss the electronic structure, orbital resolved density of states and Brillouin zone center phonons for both P4/nmm and Cmma phases along a U dependence of $\Gamma$ point phonon frequencies. [Preview Abstract] |
Monday, March 15, 2010 9:00AM - 9:12AM |
A39.00004: Electronic structure of iron-based superconductors with thick perovskite-blocking layers Hiroki Nakamura, Masahiko Machida Since superconductivity in LaFeAsO$_{1-x}$F$_x$ was found, various families of iron-based superconductors have been discovered. Recently, a new type whose blocking layer structure is perovskite-based has been reported, and Tc of this family has reached almost 40K. In this paper, we calculate electronic structures of the iron-based superconductors with thick perovskite layers by using first-principles density functional theory and compare them with those of other iron-based superconductors. We also discuss ability of application of those superconductors. [Preview Abstract] |
Monday, March 15, 2010 9:12AM - 9:24AM |
A39.00005: Electronic Structure and Magnetic Properties of CsFe$_2$Sb$_2$ David J. Singh, Lijun Zhang Iron based arsenide superconductors generally show higher critical temperatures than phosphides, while the antimonides cannot be studied because the corresponding compounds do not form. Within the ThCr$_2$Si$_2$ structure, BaFe$_2$As$_2$ and BaFe$_2$P$_2$ are known compounds, while BaFe$_2$Sb$_2$ is not. However, synthesis of CsFe$_2$Sb$_2$ was reported by Noack and Schuster in 1994. Here we report density functional studies of the electronic structure and magnetism in this material, as compared to the arsenide, KFe$_2$As$_2$. CsFe$_2$As$_2$ is found to be an antiferromagnetic metal with interesting similarities to the arsenides. [Preview Abstract] |
Monday, March 15, 2010 9:24AM - 9:36AM |
A39.00006: A Possible New Phase in Ba-Fe-As System Bing Lv, Feng Chen, Yuyi Xue, C.W. Chu A new compound in Ba-Fe-As system has been discovered. Single crystals were successfully synthesized from Sn flux. The resistivity reaches a flat minimum around 110~K, then increases drastically at $\sim$80~K and reaches a maximum at $\sim$70~K. The paramagnetic susceptibility shows a SDW-like anomaly around 80~K. The compound is also characterized by X-ray diffraction and electron microscope. The detailed structure analysis will be presented. [Preview Abstract] |
Monday, March 15, 2010 9:36AM - 9:48AM |
A39.00007: Electronic Structure, Magnetism, and Correlation Effects in Oxychalcogenide La$_2$O$_2$Fe$_2$OSe$_2$ Jian-Xin Zhu, Rong Yu, Hangdong Wang, M. Jones, Jianhui Dai, E. Abrahams, Minghu Fang, Qimiao Si Iron pnictides are the first non-copper-based compounds to exhibit high-$T_c$ superconductivity, and have therefore attracted intense interest. Whether these compounds are weakly interacting metals or bad metals near a Mott transition is a subject of extensive current discussion. Here we consider compounds containing Fe$_2$O square planar layers. The Fe-Fe distance in these systems is larger than that of their FeAs counterparts, suggesting the possibility of stronger correlation effects. We report the first-principles density functional theory (DFT) calculations on the oxychalcogenides La$_2$O$_2$Fe$_2$OSe$_2$. We have calculated the band structure and compared the results with those of the LaOFeAs compound. We have also extracted, within the GGA+$U$ approximation, the spin exchange interactions. The corresponding frustrated Heisenberg model yields a checkerboard magnetic order, which is consistent with the energetic consideration in the DFT. Finally we discuss these results in light of the experimental data from thermodynamic, transport and neutron scattering measurements. [Preview Abstract] |
Monday, March 15, 2010 9:48AM - 10:00AM |
A39.00008: Itinerant Nature of Magnetism in Iron Pnictides: A first principles study Yu-Zhong Zhang, Ingo Opahle, Harald O. Jeschke, Roser Valenti The magnetic properties of LaFe$Pn$O, BaFe$_2Pn_2$ and LiFe$Pn$ ($Pn$ = As, Sb) are investigated by using {\it ab initio} molecular dynamics based on an all-electron projector-augmented wave basis. We find that stripe-type antiferromagnetic orderings are always enhanced when As is substituted by Sb. Our calculated Pauli susceptibility strongly points towards an itinerant picture of magnetism. Furthermore, we study the lattice properties of LaFe$Pn$O ($Pn$=P, As, Sb, Bi) as well as ScFePO, ScFeAsO and YFePO and argue that LaFeSbO would be a candidate for a superconductor with highest transition temperature among the investigated compounds. [Preview Abstract] |
Monday, March 15, 2010 10:00AM - 10:12AM |
A39.00009: Structure and magnetic, thermal, and electronic transport properties of single crystal EuPd$_2$Sb$_2$ S. Das, K. McFadden, Yogesh Singh, R. C. Nath, D. C. Johnston, A. Ellern EuPd$_2$Sb$_2$ is closely related to the $A$Fe$_2$As$_2$ compounds. Single crystal x-ray diffraction studies confirmed that EuPd$_2$Sb$_2$ crystallizes in the CaBe$_2$Ge$_2$-type structure. The magnetic susceptibility and heat capacity versus temperature measurements suggest antiferromagnetic ordering at 6.0~K with the easy axis or plane in the crystallographic $ab$ plane. An additional transition occurs at 4.5~K that may be a spin reorientation transition. The 4.5~K transition is suppressed below 1.8~K while the 6.0~K transition moves down to 3.5~K in a magnetic field of $H = 8$~T. Resistivity data show metallic behavior down to 1.8~K along with an anomaly at 5.8~K in zero field. The anomaly is suppressed to 2.9~K in an 8~T field. The Hall coefficient measurements indicated that the dominant charge carriers are electrons. The magnetization $M(H)$ isotherms show three field-induced anomalies at 2.75~T, 3.90~T, and 4.2~T magnetic fields parallel to the $ab$ plane at 1.8~K\@. [Preview Abstract] |
Monday, March 15, 2010 10:12AM - 10:24AM |
A39.00010: Synthesis and Properties of CaCuAs and CaCu$_2$As$_2$ Feng Chen, Bing Lv, Yuyi Xue, C.W. Chu Motivated by the recent studies on iron pnictides, we synthesized CaCuAs and CaCu$_2$As$_2$. Single crystals of CaCuAs were also grown successfully. The resistivity, magnetic susceptibility and thermoelectric power were measured and SDW- like anomalies were observed and compared. The thermopower for both CaCuAs and CaCu$_2$As$_2$ are positive from room temperature down to 10~K, indicating holes as the majority carrier. We will report doping studies and discuss the possiblities to induce superconductivity in this system. [Preview Abstract] |
Monday, March 15, 2010 10:24AM - 10:36AM |
A39.00011: Structural and electronic properties of single-crystal Fe$_{1-x}$Co$_{x}$As K. Kirshenbaum, S. Saha, N. Butch, T. Drye, J. Magill, J. Paglione, P. Zavalij Shortly after the discovery of the iron pnictide superconductors, it was found that cobalt substitution on the iron site in the 122 ternary systems AEFe$_{2}$As$_{2}$ (AE = alkali earth) suppresses the magnetic order of the parent compounds and induces superconductivity. While transition metal substitution in the intermetallic iron arsenide superconductors is one of the most studied aspects of these materials, there is little known about the effects of substitution on the related binary system FeAs. We present transport and magnetization measurements performed on single crystals of the cobalt-substituted system Fe$_{1-x}$Co$_{x}$As, and discuss the evolution of the phase diagram of this system. [Preview Abstract] |
Monday, March 15, 2010 10:36AM - 10:48AM |
A39.00012: Large enhancement of $T_{c}$ (= 35 K) in a sample synthesized from a starting composition of LaFeAsO$_{1-y}$H$_{x}$ Kichi Miyazawa, Sigeki Ishida, Kunihiro Kihou, Parasharam M. Shirage, Hijiri Kito, Chul Ho Lee, Shinichi Uchida, Hiroshi Eisaki, Kazuyasu Tokiwa, Akira Iyo Large enhancement of superconducting transition temperature ($T_{c})$ has been found in a sample synthesized from a nominal composition of LaFeAsO$_{1-y}$H$_{x}$. A hydroxide powder of La(OH)$_{3}$ is mixed with starting materials and the sample is synthesized under high-pressure. The sample shows as high as $T_{c}$ of 35 K (susceptibility onset) and 38 K (resistivity onset), while the maximum $T_{c}$ of an oxygen-deficient LaFeAsO$_{1-y}$ is 28 K. A large contraction of lattice is observed in the hydroxide-added samples. [Preview Abstract] |
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