Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session X11: New Fe-based Superconductors and Related Materials IIFocus
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Sponsoring Units: DMP Chair: Xianhui Chen, University of Science and Technology of China Room: 307 |
Friday, March 18, 2016 8:00AM - 8:36AM |
X11.00001: Interplay of structure, magnetism and superconductivity in the 112 Fe based superconducting family Invited Speaker: Ni Ni Both cuprates and Fe-based superconductors, the two known high Tc superconducting families, show rich emergent phenomena near the superconductivity (SC). To understand the mechanism of unconventional SC, it is crucial to unravel the nature of these emergent orders. The 112 Fe pnictide superconductor (FPS), Ca1-xRExFeAs2 (CaRE112), shows SC up to 42 K, the highest bulk Tc among all nonoxide FPS [2]. Being an exceptional FPS where the global C4 rotational symmetry is broken even at room temperature, it is important to extract the similarities and differences between 112 and other FPS so that critical ingredients in inducing SC in FPS can be filtered. In this talk, I will review current progress in the study of 112. The comparison between Co doped CaLa112 and Co doped 10-3-8 will be made and the importance of interlayer coupling will be discussed. The work on 112 is supported by NSF while the work on 10-3-8 is supported by DOE. [Preview Abstract] |
Friday, March 18, 2016 8:36AM - 8:48AM |
X11.00002: Structural symmetries of the 112-type iron-based superconductor (Ca$_{1-x}$La$_x$)FeAs$_2$ studied using nonlinear and ultrafast optics John Harter, Hao Chu, Shan Jiang, Ni Ni, David Hsieh The crystal structure of the newly discovered 112-type iron-based superconductors contains symmetry-breaking arsenic chains, avoiding the need for local probes or uniaxial strain in order to study the ubiquitous electronic nematic state that exists in the vicinity of magnetic order in the iron pnictides. In addition, the 112-type materials are the first known high-temperature superconductors without a center of inversion, with interesting ramifications for Cooper pairing in the superconducting state. We present details of the structure of 112-type (Ca$_{1-x}$La$_x$)FeAs$_2$ using rotational anisotropy second harmonic generation and pump-probe transient reflectivity experiments. These all-optical techniques are complimentary to conventional diffraction measurements and enable a precise determination of crystallographic symmetries. Our measurements highlight the novel structural properties of the 112-type materials. [Preview Abstract] |
Friday, March 18, 2016 8:48AM - 9:00AM |
X11.00003: ABSTRACT WITHDRAWN |
Friday, March 18, 2016 9:00AM - 9:12AM |
X11.00004: The Interplay of Fe and Ce Magnetism in Ca$_{0.71}$ Ce$_{0.29}$(Fe$_{1-x}$Co$_x$)As$_2$ single crystals Shan Jiang, Lian Liu, Huibo Cao, Wei Tian, Eve Emmanuelidu, Aoshuang Shi, Yasutomo Uemura, Ni Ni In this talk, we will present the synthesis and characterization of the Ca$_{0.71}$ Ce$_{0.29}$(Fe$_{1-x}$Co$_x$)As$_2$ single crystals. Elastic neutron scattering complemented by resistivity, susceptibility and heat capacity measurements has revealed a paramagnetic-to-antiferromagnetic phase transition of the Fe sublattice at 69K and a monoclinic-to-triclinic structural phase transition at 73 K in Ca$_{0.71}$ Ce$_{0.29}$FeAs$_2$. In addition, Fe spin reorientation and Ce ordering at lower temperatures, reminiscent of the one in REFeAsO (RE=Ce, Pr, Nd) materials, exist. The Co substitution on the Fe sites completely suppresses the ordering of Fe sublattice at x=0.032. However, it only slightly affects the Ce ordering, which prevents the formation of superconductivity in Ca$_{0.71}$ Ce$_{0.29}$(Fe$_{1-x}$Co$_x$)As$_2$. [Preview Abstract] |
Friday, March 18, 2016 9:12AM - 9:24AM |
X11.00005: Thallium-doped BaFe$_{\mathrm{2}}$As$_{\mathrm{2}}$ crystals: The unusual competition between magneto-elastic coupling and charge doping Athena Sefat, Li Li, Huibo Cao, Brian Sales, Michael McGuire, Radu Custelcean, David Parker We partially substitute thallium for barium and report the effects of interlayer coupling in Ba$_{\mathrm{1-x}}$Tl$_{\mathrm{x}}$Fe$_{\mathrm{2}}$As$_{\mathrm{2}}$ crystals. We demonstrate the unusual competition between magneto-elastic coupling and charge doping in an iron-arsenide material, whereby $T_{N}$ temperature rises in BaFe$_{\mathrm{2}}$As$_{\mathrm{2}}$, and then falls with additional Tl-doping. Evidence from temperature-dependent bulk thermodynamic and transport properties, and neutron diffraction results will be presented. Using LDA, we illustrate that small changes related to 3$d$ transition-metal state can have profound effects on magnetism. [Preview Abstract] |
Friday, March 18, 2016 9:24AM - 9:36AM |
X11.00006: Structural and antiferromagnetic properties of Ba(Fe$_{\mathrm{1-}}_{x}_{\mathrm{-}}_{y}$Co$_{x}$Rh$_{y})_{\mathrm{2}}$As$_{\mathrm{2}}$ compounds Min Gyu Kim, T. W. Heitmann, S. R. Mulcahy, E. D. Bourret-Courchesne, R. J. Birgeneau We present a systematic investigation of the electrical, structural, and antiferromagnetic properties for the series of Ba(Fe$_{\mathrm{1-}}_{x}_{\mathrm{-}}_{y}$Co$_{x}$Rh$_{y})_{\mathrm{2}}$As$_{\mathrm{2}}$ compounds with fixed $x \quad =$ 0.027 and 0 \textless $y$ \textless 0.035. We compare our results for the Co-Rh doped Ba(Fe$_{\mathrm{1-}}_{x}_{\mathrm{-}}_{y}$Co$_{x}$Rh$_{y})_{\mathrm{2}}$As$_{\mathrm{2}}$ compounds with Ba(Fe$_{\mathrm{1-}}_{x}$Co$_{x})_{\mathrm{2}}$As$_{\mathrm{2}}$ compounds. We demonstrate that the electrical, structural, antiferromagnetic, and superconducting properties of the Co-Rh doped compounds are similar to the properties of the Co doped compounds. We find that the overall behaviors of Ba(Fe$_{\mathrm{1-}}_{x}_{\mathrm{-}}_{y}$Co$_{x}$Rh$_{y})_{\mathrm{2}}$As$_{\mathrm{2}}$ and Ba(Fe$_{\mathrm{1-}}_{x}$Co$_{x})_{\mathrm{2}}$As$_{\mathrm{2}}$ compounds are very similar when the total number of the extra electrons per Fe/\textit{TM} (\textit{TM} $=$ transition metal) site is considered, which is consistent with the rigid band model. Despite the similarity, we find that the details of the transitions are different in between Ba(Fe$_{\mathrm{1-}}_{x}_{\mathrm{-}}_{y}$Co$_{x}$Rh$_{y})_{\mathrm{2}}$As$_{\mathrm{2}}$ and Ba(Fe$_{\mathrm{1-}}_{x}$Co$_{x})_{\mathrm{2}}$As$_{\mathrm{2}}$ compounds. [Preview Abstract] |
Friday, March 18, 2016 9:36AM - 9:48AM |
X11.00007: Search for New Superconductors: An Electro-Magnetic Phase Transition in an Iron Meteorite Inclusion at 117 K Stefan Gu\'enon, Juan Gabriel Ramirez, Ali C. Basaran, Jamie Wampler, Mark Thiemens, Ivan K. Schuller We investigated a natural iron sulfide based materials (Troilite) inclusion with its associated minerals in the iron meteorite Tlacotepec. The search for superconductivity in these heterogeneous materials requires a technique capable of detecting minute amounts of a superconducting phase embedded in a non-superconducting matrix. We used Magnetic Field Modulated Microwave Spectroscopy (MFMMS), a very sensitive, selective, and non-destructive technique, to search for superconductivity in heterogeneous systems. Here, we report the observation of an electro-magnetic phase transition at 117 K that causes a MFMMS-response typical of a superconductor. A pronounced and reproducible peak together with isothermal magnetic field sweeps proves the appearance of an electromagnetic phase below 117 K. This is very similar to the characteristic response due to flux trapping in a granular superconductor with a short coherence length. This work was supported by the AFOSR under the grant number AFOSR-MURI FA9550-14-1-0202. [Preview Abstract] |
Friday, March 18, 2016 9:48AM - 10:00AM |
X11.00008: Heisenberg Model Analysis on Inelastic Powder Neutron Scattering Data Using Pure and K doped BaMn2As2 samples Mehmet Ramazanoglu, A. Sapkota, A. Pandey, D. Johnston, Alan Goldman, A. Kreyssig, D. Abernathy, J. Niedziela, M. Stone, R.J. McQueeney Low temperature powder inelastic neutron scattering measurements (INS) were performed on powders of Ba(1-x)KxMn2As2 with x=0(BMA),0.125 and 0.25. BMA is a G type antiferromagnet (AFM) which has local magnetic modulations bridging between the pnictide and cuprate superconductors. Hole doping (K) introduces more metallic behavior. The magnetic contribution to the intensities were retrieved by subtracting the estimated phonon background obtained at high momentum transfers from the raw. The resultant estimated magnetic intensities were analyzed by using damped harmonic oscillator model. The K doping effects create a broadening in the magnetic peak profiles consistent with expected weak FM fluctuations. We also analyzed the INS data using a powder integration routine which is based on J1-J2-Jz Heisenberg Model. The Monte Carlo integration technique is used to obtain the powder-averaged S(Q,E) for a series of Js. The representative values (with lowest chi-squared) obtained for BMA are in agreement with previous results. The values obtained for K doped samples were found in the close proximity to the parent ones. Overall we conclude that the original AFM structure seen in BMA retained its character even in the K doped samples with minimal differences. [Preview Abstract] |
Friday, March 18, 2016 10:00AM - 10:12AM |
X11.00009: A new class of half-metallic ferromagnets based on the pnictide superconductors from first principles. Sinead Griffin, Jeffrey Neaton Most theoretical and experimental efforts in the Fe-pnictide class of superconductors aim to optimize the superconducting Tc. Significant substitution with other transition-metal ions is detrimental to superconductivity, however recent experiments on doped BaMn$_{2}$As$_{2}$ point to its potential as a half-metallic ferromagnet. Using ab initio calculations we investigate Mn-based structures as a new family of half-metallic ferromagnets, and discuss tuning the chemical composition and physical parameters for optimal device performance. [Preview Abstract] |
Friday, March 18, 2016 10:12AM - 10:24AM |
X11.00010: Antiferromagnetism in CaAl$_2$Si$_2$-type CaMn$_2$As$_2$ and SrMn$_2$As$_2$ single crystals$^{\ast}$ N. S. Sangeetha, Abhishek Pandey, Zackery A. Benson, D. C. Johnston Magnetic susceptibility versus temperature $\chi(T)$ measurements of $\rm{CaMn_2As_2}$ and $\rm{SrMn_2As_2}$ crystals show clear antiferromagnetic (AFM) transitions at $T_{\rm{N}}\approx 65$ K and 120 K,$^{1}$ respectively. The anisotropic behaviors in $\chi(T\leq T_{\rm{N}})$ suggest that both compounds are noncollinear antiferromagnets which may result either from an intrinsic noncollinear structure or from multiple collinear AFM domains that are not aligned collinearly.$^{2}$ The $\chi(T)$ data at $T>T_{\rm{N}}$ reveal that both compounds exhibit strong short-range AFM ordering, evidently associated with quasi-two-dimensional spin lattices. The electrical resistivities show insulating ground states with activation energies of $\approx 63$ meV in $\rm{CaMn_2As_2}$ and 44 meV in $\rm{SrMn_2As_2}$. The experimental results thus reveal that both $\rm{(Ca,Sr)Mn_2As_2}$ materials are AFM insulators at low temperatures and in analogy with the high $T_{\rm{c}}$ cuprates, may be potential parent compounds for CaAl$_2$Si$_2$-type superconductors.$\\^{\ast}$Work was supported by the USDOE under Contract No. DE-AC02-07CH11358.$\\^{1}$Z.W. Wang et. al, J. Phys. Chem. Solids $\mathbf{72}$, 457 (2011).\\$^{2}$D. C. Johnston, PRL \textbf{109}, 077201 (2012); PRB \textbf{91}, 064427 (2015). [Preview Abstract] |
Friday, March 18, 2016 10:24AM - 10:36AM |
X11.00011: Resistivity Anisotropy in Single Crystals of CaCo$_{1.86}$As$_2$ M. A. Tanatar, V. K. Anand, A. Pandey, N. S. Sangeetha, D.C. Johnston, R. Prozorov In-plane and inter-plane resistivity was measured in single crystals of type A antiferromagnet CaCo$_{2-x}$As$_2$ ($x=$ 0.14). Clear anomalies in the temperature dependent resistivity are observed at the magnetic ordering at $T_N \approx$50~K. The transition shifts to lower temperatures upon application of 9 T magnetic field both along tetragonal (001) axis, $H \parallel c$, and transverse to it, $H \bot c$. The temperature – - magnetic field phase diagrams determined from the resistivity measurements are in good agreement with magnetization measurements [1]. No additional anomalies are found at the spin-flop transition in the compound, suggesting that the direction of the spin does not play an appreciable role in the spin-disorder scattering in this compound. [1] V.~K.~Anand {\it et al.} Phys. Rev B {\bf 89}, 214409 (2014). [Preview Abstract] |
Friday, March 18, 2016 10:36AM - 10:48AM |
X11.00012: \textbf{Wall-like spin excitations in A-type antiferromagnetic CaCo}$_{\mathrm{\mathbf{2}}}$\textbf{As}$_{\mathrm{\mathbf{2}}}$ A. Sapkota, B. G. Ueland, Abhishek Pandey, D. C. Johnston, A. Kreyssig, R. J. McQueeney, A. I. Goldman, V. K. Anand, J. L. Niedziela, D. L. Abernathy The $A$Co$_{\mathrm{2}}$As$_{\mathrm{2\thinspace }}(A =$ Ca, Sr, Ba ) compounds are structurally and chemically similar to $A$Fe$_{\mathrm{2}}$As$_{\mathrm{2\thinspace }}$and possess some interesting similarities and differences in their magnetism. We recently discovered that SrCo$_{\mathrm{2}}$As$_{\mathrm{2}}$ has stripe antiferromagnetic (AFM) spin correlations similar to stripe-ordered $A$Fe$_{\mathrm{2}}$As$_{\mathrm{2}}$. On the other hand, CaCo$_{\mathrm{2}}$As$_{\mathrm{2}}$ orders in an A-type AFM structure with ferromagnetic correlation of the spins in the square-lattice Co-layer and AFM correlations between layers. Despite the A-type order, our recent inelastic neutron scattering measurements show that spin excitations in CaCo$_{\mathrm{2}}$As$_{\mathrm{2}}$ are not associated with either the A-type or stripe-type order. Instead, we observe broad excitations that extend longitudinally (along (1,1,0) in reciprocal space), but remain sharply defined in the transverse direction. These excitations seem to be best characterized as a ``wall'' of scattering and suggest that CaCo$_{\mathrm{2}}$As$_{\mathrm{2}}$ has quasi-one-dimensional spin dynamics very different than in $A$Fe$_{\mathrm{2}}$As$_{\mathrm{2}}$ and SrCo$_{\mathrm{2}}$As$_{\mathrm{2}}$. [Preview Abstract] |
Friday, March 18, 2016 10:48AM - 11:00AM |
X11.00013: Pressure-induced collapsed-tetragonal phase in SrCo$_{2}$As$_{2}$ at ambient temperature W. T. Jayasekara, U. S. Kaluarachchi, B. G. Ueland, A. Pandey, Y. B. Lee, V. Taufour, A. Sapkota, K. Kothapalli, N. S. Sangeetha, S. L. Bud'ko, B. N. Harmon, P. C. Canfield, D. C. Johnston, A. Kreyssig, A. I. Goldman, G. Fabbris, Y. Feng, L. S. I. Veiga, A. M. dos Santos Our recent high-energy (HE) high-pressure (HP) x-ray powder diffraction measurements on tetragonal (T) SrCo$_{2}$As$_{2}$ have revealed a first-order pressure-induced structural phase transition to a collapsed tetragonal (cT) phase with a reduction in $c$ by -7.9\% and the $c/a$ ratio by -9.9\%. The T and cT phases coexist for applied pressures 6~GPa to 18~GPa at 7~K. Resistance measurements up to 5.9 GPa and down to 1.8 K signatures likely associated with the cT phase above 5.5 GPa and found no evidence for superconductivity. Neutron diffraction data show no evidence of magnetic order up to 1.1 GPa. Here, we show that the T to cT transition occurs around 6.8 GPa at ambient temperature, and that the transition is nearly temperature-independent from 300~K down to 7~K, which indicates a steep $p-T$ phase line.\\ Work at Ames Lab. was supported by US DOE, BES, DMSE under DE-AC02-07CH11358. This research used resources at the APS and ORNL, US DOE, SC, User Facilities. [Preview Abstract] |
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