Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session D23: Focus Session: Search for New Superconductors I: Exploring Emergent Phases |
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Sponsoring Units: DMP Chair: David Mandrus, Oak Ridge National Laboratory Room: D165 |
Monday, March 21, 2011 2:30PM - 2:42PM |
D23.00001: Phase Transitions in CuAs-based K$_{x}$Sr$_{1-x}$Cu$_{4}$As$_{2}$ System Bing Lv, Bernd Lorenz, Melissa Gooch, Feng Chen, Liangzi Deng, Ching-Wu Chu Inspired by the superconductivity with a T$_{c }\sim $ 3.5 K reported by Han et al. in Cu-based LiCu$_{2}$P$_{2}$, the Cu-based compound SrCu$_{4}$As$_{2, }$which has a more complex CuAs layers structure sandwiched by Sr layers, was synthesized and characterized. The magnetoresistance measurements show two anomalies around $\sim $140K and $\sim $60K, respectively, which is also consistent with the results of specific heat measurement. Systematically studies of K-doping into SrCu$_{4}$As$_{2}$ system are carefully investigated at ambient and high pressures and no superconductivity has been found in the K$_{x}$Sr$_{1-x}$Cu$_{4}$As$_{2}$ system down to 2K, although superconductivity might occur at lower temperature in this system. The overall pressure and doping effects on the magnetic and transport properties of the compounds will be presented and discussed. [Preview Abstract] |
Monday, March 21, 2011 2:42PM - 2:54PM |
D23.00002: Synthesis and Characterization of ACu$_{4}$Pn$_{2}$, with A = alkaline and Pn = As and Sb L.Z. Deng, Bing Lv, Y.Y. Xue, C.W. Chu A large number of the Cu-based layer compounds have been known to exist since the 1970's: some display structures similar to the Fe-based pnictide superconductors, such as the 111 and 122 phases. Unfortunately, other than their structures, reports on their physical properties are generally sparse. Only recently observation of superconductivity with a T$_{c }\sim $ 3.5 K was reported by Han et al. in LiCu$_{2}$P$_{2}$ that displays a 122 structure. It was suggested that a more complex layer structure in pnictides may favor higher T$_{c}$ as in the case of cuprates. We have therefore examined systematically ACu$_{4}$Pn$_{2}$ (142), with A = alkaline and Pn = pnictigen which has a more complicated layer substructure than the 1111, 111, 122 or 11 homologues. We have synthesized ACu$_{4}$Pn$_{2}$, with A = Li, Na, K, Rb and Cs and Pn = As and Sb, some of which were made for the first time. The magnetic, electrical, calorimetric and thermal electric properties were determined at ambient pressure and compared. High pressure was also applied to some of the compounds. The results will be presented and discussed. [Preview Abstract] |
Monday, March 21, 2011 2:54PM - 3:06PM |
D23.00003: Superconductivity and Competing Ordered Phase in RuPn (Pn = As, P) Daigorou Hirai, Tomohiro Takayama, Daisuke Hashizume, Ayako Yamamoto, Hidenori Takagi Unconventional superconductivity likely manifests itself when some competing electronic phases are suppressed down to zero temperature such as cuprates and iron-pnictide superconductors. Therefore, the correlated metallic state neighboring a competing electronic ordering can be a promising playground for unconventional superconductivity. Here we report superconductivity emerging adjacent to electronically ordered phases of RuPn (Pn = As, P). We found that RuAs(P) exhibits phase transitions at 240 (265) K, which is discerned as a drop of magnetic susceptibility or a resistivity upturn. Such anomalies can be suppressed by substituting Rh to the Ru site. Accompanied by the disappearance of the electronic order, superconductivity was found to emerge below 1.8 K and 3.8 K for RuAs and RuP, respectively. The superconductivity in Rh substituted RuPn, which neighbors a competing electronic order, might exhibit an exotic pairing state as seen in the unconventional superconductors known to date. [Preview Abstract] |
Monday, March 21, 2011 3:06PM - 3:42PM |
D23.00004: Towards New and Higher Temperature Superconductors via Theory Assisted Synthesis Invited Speaker: We discuss here a new methodology where electronic structure calculations are integrated with the synthesis of new superconducting materials, with the objective to design and realize new lamellar superconductors with high onset temperatures, and to rigorously test the apparent association of high temperature superconductivity with electron delocalization transitions occurring at quantum critical points. Since lamellar superconductors like the cuprates and iron pnictides are comprised of functional layers where superconductivity resides and charge reservoir layers that determine the electron count in the functional layers, we will use realistic electronic structure calculations to assess which transition metal monopnictides are closest to electron delocalization, and hence optimal for superconductivity. Optical conductivity and photoemission measurements will be used to compare the real and calculated electronic structures. We report initial results on electron and hole doped LaMnPO. [Preview Abstract] |
Monday, March 21, 2011 3:42PM - 3:54PM |
D23.00005: Gap physics of the doped semiconductor (Ca,F):LaMnPO J.W. Simonson, M.C. Aronson Single crystals of Ca$_{x}$La$_{1-x}$MnPO and LaMnPO$_{1-y}$F$_{y}$ (x = 0 to 0.50, y = 0 to 0.40) were synthesized to study the effect of Ca and F doping on LaMnPO, which is isostructural with several recently discovered Fe-based superconductors. The inclusion of F into the lattice was confirmed with single crystal XRD, showing a systematic reduction in unit cell volume with dopant content, in agreement with published accounts of similar compounds. Little change from undoped LaMnPO was observed in the resistivity of Ca doped crystals, while doping with successively higher concentrations of F yielded a systematic enhancement of conductivity. Nonetheless, all resistivity measurements were semiconducting, suggesting that E$_{F}$ remains pinned within the gap regardless of dopant concentration. Activated behavior was observed, with activation energies falling below 100 meV, substantially less than the ~1 eV optical gap. At low temperatures, the resistivity of all compositions exhibited temperature dependence in accord with variable range hopping, suggesting that transport is dominated by disordered and localized states at the Fermi level. [Preview Abstract] |
Monday, March 21, 2011 3:54PM - 4:06PM |
D23.00006: Properties of layered iron oxychalcogenides with checkerboard structure Liang L. Zhao, Daniel Ward, Douglas Natelson, Emilia Morosan The layered iron oxychalcogenides La$_2$O$_3$Fe$_2$X$_2$ (X = S, Se) have a unique checkerboard-like Fe$_2$OX$_2$ sublattice. Their Mott insulating behavior makes them promising candidates for novel superconductors. In this talk, we present results on the isostructural A$_2$F$_2$Fe$_2$OS$_2$ (A = Sr, Ba) compounds. Both pure and doped samples are characterized by magnetization, resistivity, heat capacity and Raman spectroscopy measurements. In addition to the previously reported antiferromagnetic transition around T$_N~\approx$ 100 K, we observed another phase transition in the ordered state, as well as a possible structural phase transition near room temperature. A change in the excitation gap at the high temperature (structural) phase transition is indicated by the temperature dependent resistivity. [Preview Abstract] |
Monday, March 21, 2011 4:06PM - 4:18PM |
D23.00007: Development of high-temperature solutions for the crystal growth of calchogenide and pnictide bearing compounds Xiao Lin, Rongwei Hu, Sergey Bud'ko, Paul Canfield With the discovery of superconductivity in the FeAs and FeSe/S based materials and proposed topological insulators in a variety of Te and Se based compounds the need to develop crystal growth techniques that readily incorporate and simultaneously control volatile (and often toxic) elements is of growing importance. In this talk we will review our initial efforts to develop versatile solution growth techniques for single crystal growth of P, As, S, Se and/or Te containing compounds. We will present our results on our use of S-bearing solutions to grow binary and ternary sulphides as well as the development of hybrid solutions the components of which each allow for the incorporation of hard to dissolve elements. [Preview Abstract] |
Monday, March 21, 2011 4:18PM - 4:30PM |
D23.00008: ABSTRACT WITHDRAWN |
Monday, March 21, 2011 4:30PM - 4:42PM |
D23.00009: Bulk superconductivity in intercalated M$_{x}$ZrTe$_{3}$ (M=Cu, Ni) Xiangde Zhu, Hechang Lei, Cedomir Petrovic We report the bulk superconductivity of 3d transition metal (e.g. Cu, Ni) intercalated ZrTe$_{3}$ single crystals, M$_{x}$ZrTe$_{3}$ (M=Cu, Ni). ZrTe3 shows charge density wave (CDW) transition at T$_{CDW}$=63K and the CDW nesting vector q$_{CDW}$=(1/14,0,1/3) (reciprocal space). It is metallic below 300K with an anomaly due to CDW transition and becomes filamentary superconductor below 2 K. The derived superconducting parameters indicate that M$_{x}$ZrTe$_{3}$ are bulk type-II superconductors and can be depicted in the framework of Bardeen-Cooper-Schrieffer (BCS) scenario. Intercalation depresses the CDW transition and enhances the superconductivity. [Preview Abstract] |
Monday, March 21, 2011 4:42PM - 4:54PM |
D23.00010: New layered oxuchalcogenide La$_{2}$O$_{2}$Mn$_{2}$OSe$_{2}$ Hechang Lei, Cedomir Petrovic We report a new La$_{2}$O$_{2}$Mn$_{2}$OSe$_{2}$ and investigate its physical properties. It is a member of Ln$_{2}$O$_{2}$Tm$_{2}$OCh$_{2}$ (Ln= rare earth, Tm=Fe, Co, and Ch=S, Se). The structure of these compounds can be described as an alternate stacking of fluorite type [Ln$_{2}$O$_{2}$]$^{2+}$ or [A$_{2}$F$_{2}$]$^{2+}$ layers and anti-CuO$_{2}$-type [Tm$_{2}$OCh$_{2}$]$^{2-}$ layers (anti-perovskite type). La$_{2}$O$_{2}$Mn$_{2}$OSe$_{2}$ is the first manganese-base compound with anti-CuO$_{2}$-type layers. It is a ferromagnetic (FM) Mott insulator exhibiting several successive magnetic transitions. The magnetic properties are different from other compounds with this structure. [Preview Abstract] |
Monday, March 21, 2011 4:54PM - 5:06PM |
D23.00011: Physical Properties of CaFe$_{4}$As$_{3}$ Single Crystals Amar Karki, Yimin Xiong, Jianneng Li, Shane Stadler, Gregory McCandless, Julia Chan, Rongying Jin New compound CaFe$_{4}$As$_{3}$ crystallizes in an orthorhombic structure with Fe$_{2}$As$_{2}$ layers aligned along $b$ direction but a rectangular cross-section in \textit{ac} plane. The needle-shaped CaFe$_{4}$As$_{3}$ single crystals were grown and are found to undergo two successive phase transitions occurring at T$_{1} \sim $ 90 K and T$_{2} \sim $ 27 K, respectively. At T$_{1}$ the electrical resistivity increases and magnetic susceptibility decreases in both parallel and perpendicular to $b$ directions consistent with the scenario of spin-density-wave formation. At T$_{2}$, resistivity decreases sharply at T$_{2}$ with hysteresis while magnetic susceptibility increases along either $b$ direction or \textit{ac} plane. The underlying physics will be discussed by taking into account other physical properties. [Preview Abstract] |
Monday, March 21, 2011 5:06PM - 5:18PM |
D23.00012: Superconductivity in SnO: a Nonmagnetic Analogue to Fe-based Superconductors Daniel Khomskii, M.K. Forthaus, K. Sengupta, O. Heyer, N.E. Christensen, A. Svane, K. Syassen, T. Lorenz, M.M. Abd-Elmeguid We found that under pressure SnO with $\alpha $-PbO structure, the same structure as in many Fe-based superconductors, e.g. $\beta $-FeSe, undergoes a transition to a superconducting state for p $\ge $ 6 GPa with a maximum T$_{c}$ of 1.4 K at p = 9.3 GPa. The pressure dependence of T$_{c}$ reveals a dome-like shape and superconductivity disappears for p $>$ 16 GPa. It is further shown from band structure calculations that SnO under pressure exhibits a Fermi surface topology similar to that reported for some Fe-based superconductors and that the nesting between the hole and electron pockets correlates with the change of T$_{c}$ as a function of pressure. M.K. Forthaus et al., Phys.Rev.Lett. \textbf{105}, 15701 (2010) [Preview Abstract] |
Monday, March 21, 2011 5:18PM - 5:30PM |
D23.00013: Development of iron pnictides with very thick perovskite-type blocking layers Hiraku Ogino, Shinya Sato, Naoto Kawaguchi, Yasuaki Shimizu, Kenji Machida, Akiyasu Yamamoto, Kohji Kishio, Jun-ichi Shimoyama Recently we have discovered several new layered iron pnictides having extremely thick blocking layers [1]. These compounds have up to 5 sheets of perovskite-type layers between iron pnictide layers. Similar to LiFeAs, these compounds showed bulk superconductivity without intensive carrier doping, and the Tc of the compounds are 40 K-class. On the other hand, the relationship between Tc and the iron-plane interlayer distance suggested that Tc of the iron based superconductor is basically determined by the local structure of Fe2As2 layer. It is thought that there is still considerable room for the development of new layered iron pnictide compounds, due to the structural and chemical flexibility of the blocking layer. However, the results suggest that optimization of the local structure of Fe2As2 layers and the dimensionality of the crystal structure may not lead to further enhancement of Tc. Their structural features as well as physical properties will be presented.\\[4pt] [1] H. Ogino et al., APL 97 (2010) 072506 [Preview Abstract] |
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