Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session B40: Focus Session: Iron Based Superconductors Physical Properties I |
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Sponsoring Units: DCMP Chair: Rongying Jin, Louisiana State University Room: F151 |
Monday, March 15, 2010 11:15AM - 11:27AM |
B40.00001: Unusual Temperature and Field Dependence of Electrical Resistivity of Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ Ying Yang, Rongying Jin, A.S. Sefat, M.A. McGuire, B.C. Sales, D. Mandrus The in-plane electrical resistivity ($\rho _{ab})$ of Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ single crystals with x=0.02 and 0.20 was measured as a function of temperature (2 - 400 K) and magnetic field (up to 14 Tesla). At the under-doped end (x = 0.02) of the superconductivity dome, we observe positive transverse (H$\bot $\textit{ab}) magnetoresistance (MR) that varies linearly with H, and T$^{2 }$dependence of $\rho _{ab}$ below and above the structure transition temperature. Surprisingly, the negative MR and T$^{1.5}$ dependence of $\rho _{ab}$ were found for the over-doped end member (x=0.2). The underlying physics of such unusual temperature and field dependence of $\rho _{ab}$ will be discussed. [Preview Abstract] |
Monday, March 15, 2010 11:27AM - 11:39AM |
B40.00002: A Semimetal Model of the Normal State Susceptibility and Transport Properties of Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ Superconductors Brian Sales, Athena Sefat, Michael McGuire, David Mandrus A simple two-band 3D model of a semimetal is constructed to see which normal state features of the Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ superconductors can be qualitatively understood within this framework. The model is able to account in a semiquantitative fashion for the measured magnetic susceptibility, Hall, and Seebeck data, and the low temperature Sommerfeld coefficient for 0 $<$x$<$0.3 with only 3 parameters for all x. The purpose of the model is not to fit the data but to provide a simple starting point for thinking about the physics of these interesting materials. Although many of the static magnetic properties, such as the increase of the magnetic susceptibility with temperature, are reproduced by the model, none of the spin-fluctuation dynamics are addressed. A general conclusion from the model is that the magnetic susceptibility of most semimetals should increase with temperatures. This is indeed found to be the case for two well-known semimetals Bi and TiSe$_{2}$. Research supported by the US DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering. [Preview Abstract] |
Monday, March 15, 2010 11:39AM - 11:51AM |
B40.00003: Thermoelectric power and Hall coefficient measurements on Ba(Fe$_{1-x}$TM$_x$)$_2$As$_2$ ( TM=Co and Cu) Paul C. Canfield, Eundeok Mun, Ni Ni, Alex N. Thaler, Sergey L. Bud'ko Temperature-dependent thermoelectric power (TEP) data on Ba(Fe$_{1-x}$TM$_x$)$_2$As$_2$ (TM=Co and Cu), complemented by the Hall coefficient data on the samples from the same batches, have been measured. For Co doping we clearly see a change in the temperature-dependent TEP and Hall coefficient data when the sample is doped to sufficient $e$ (the number of extra electrons associated with the TM doping) so as to stabilize low-temperature superconductivity. Remarkably, a similar change is found in the Cu- doped samples at a comparable $e$ value, even though these compounds do not superconduct. These changes possibly point to a significant modification of the Fermi surface/band structure of Ba(Fe$_{1-x}$TM$_x$)$_2$As$_2$ at small electron doping, that in the case of Co doping is just before, and probably allows for, the onset of superconductivity. These data are also consistent with recent ARPES results showing changes in Fermi-surface at similar $e$ values.[1] // [1]C. Liu et al. arXiv:0910.1799 (2009) [Preview Abstract] |
Monday, March 15, 2010 11:51AM - 12:03PM |
B40.00004: High-Temperature Electrical and Magnetic Properties of Undoped Iron Pnicties Jianneng Li, Y. Yang, R. Jin, J.R. Thompson, H. Wang, B.C. Sales, A.S. Sefat, M.A. McGuire, V. Keppens, D. Mandrus We have investigated the electrical and magnetic properties of several parent compounds of Fe-based superconductors in a wide temperature range. In addition to the well-known transitions (one structural transition at T$_{s}$ and one spin-density-wave (SDW) transition at T$_{M})$, all investigated parent compounds (BaFe$_{2}$As$_{2}$,$_{ }$SrFe$_{2}$As$_{2}$, LaFeAsO, FeTe) show unusual features in both magnetic susceptibility and electrical resistivity at high temperatures (T). Above T$_{s}$, their magnetic susceptibility increases more or less linearly with increasing temperature up to at least 700 K. On the other hand, the electrical resistivity exhibits non-monotonic temperature dependence, revealing non-metallic character at high temperatures. The implication of these results will be discussed. [Preview Abstract] |
Monday, March 15, 2010 12:03PM - 12:15PM |
B40.00005: Study of the carrier content, scattering processes and the magnetic transition in Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2} $ single crystals by transport measurements Florence Rullier-Albenque, Doroth\'ee Colson, Anne Forget, Henri Alloul We present resistivity $\rho(T)$ and Hall effect measurements in Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ single crystals for a large range of Co dopings $x$ [1]. The negative Hall constant R$_{H}$ measured whatever $x$ indicates that electrons always dominate the transport properties at all $T$. More precisely, the analysis of our data at low $T$ indicates that the Hall number $n_{H}$($T$)=1/$e R_{H}$ can be assimilated to the actual values of electron content for $x > 0.04$, in good agreement with ARPES measurements on the same samples [2]. We also show that the electron carriers have archetypal Fermi liquid behavior, with large $T^{2}$ contributions to the electron scattering rate $1/\tau_{e}$. We propose that the unusually large variations of carrier content for $T < 150$K and of $1/\tau_{e}$ might be assigned to the small values of $E_{F}$ found in these compounds. In all the magnetic samples, the spin density wave transition is signalled by a drop in $n_{H}$ resulting from the gap opening associated with the nesting between the electron and hole bands. Moreover the evolution of $R_{H}(T)$ found for low Co dopings indicates that important modifications of the band structure of BaFe$_{2}$As$_{2}$ happen before the emergence of superconductivity at $x > 3$\%. [1] F. Rullier-Albenque et al., Phys. Rev. Lett. \textbf{103}, 057001 (2009). [2] V. Brouet et al., Phys. Rev. B \textbf{80},165115 (2009). [Preview Abstract] |
Monday, March 15, 2010 12:15PM - 12:27PM |
B40.00006: Structural and physical properties of Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ single Crystals Alexander Thaler, Ni Ni, Alfred Kracher, Jiaqiang Yan, Sergey Bud'ko, Paul Canfield Single crystals of Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$, $x<0.4$, have been grown and characterized by compositional, structural, magnetic and transport measurements. These measurements show that the structural/magnetic phase transition found in pure BaFe$_2$As$_2$ at 134K is suppressed monotonically by Ru doping. Superconductivity is stabilized at low temperatures for $x>0.2$ and continues through the highest doping levels we have been able to produce. The superconducting region is dome like, with maximum T$_c\sim18$K found for $x \sim 0.25$. The phase diagram of temperature versus doping based on our measurements will be compared to those of the Ba(Fe$_{1-x}$TM$_x$)$_2$As$_2$ (TM=Co, Ni, Rh, Pd) series as will the associated changes in unit cell dimension and volume. Since Ru doping does not provide extra electrons, the T-x phase diagram will also be compared with T-P phase diagram of pure BaFe$_2$As$_2$. [Preview Abstract] |
Monday, March 15, 2010 12:27PM - 1:03PM |
B40.00007: Phase diagrams and physical properties of Ba(Fe$_{1-x}$TM$_x$)$_2$As$_2$ (TM = Co, Ni, Cu, Rh, Pd) Invited Speaker: A brief overview and summary of the effects of transition metal (Co, Ni, Cu, Pd, and Rh) doping on physical properties of BaFe$_2$As$_2$ will be presented. A comparison of the phase diagrams for different dopants will be examined in detail. A range of experimental parameters that allow for the stabilization of superconductivity will be outlined. The evolution of physical properties with doping, in particular, a possible Lifshitz transition at low doping as inferred from thermoelectric power and Hall measurements (as well as ARPES) will be examined. In addition, a ``universal'' behavior of specific heat jump at $T_c$ will be discussed. [Preview Abstract] |
Monday, March 15, 2010 1:03PM - 1:15PM |
B40.00008: In-plane electronic anisotropy in underdoped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ revealed by detwinning in a magnetic field Jiun-Haw Chu, James Analytis, David Press, Kristiaan De Greve, Thaddeus Ladd, Yoshihisa Yamamoto, Ian Fisher We present results of angle-dependent magnetoresistance measurements and direct optical images of underdoped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ which reveal partial detwinning by action of a 14T magnetic field. Driven by a substantial magneto-elastic coupling, this result provides evidence for an electronic origin of the lattice distortion in underdoped iron pnictides. The observed anisotropy in these partially detwinned samples implies a substantial in-plane electronic anisotropy in the broken symmetry state, with a smaller resistivity along the antiferromagnetic ordering direction. [Preview Abstract] |
Monday, March 15, 2010 1:15PM - 1:27PM |
B40.00009: Non-Fermi Liquid Transport Properties in Phosphorous Substituted Iron-Arsenides Shigeru Kasahara, Takasada Shibauchi, Kenichiro Hashimoto, Minoru Yamashita, Hiroaki Shishido, Ryuji Okazaki, Hiroaki Ikeda, Takahito Terashima, Yuji Matsuda The anomalous normal-state charge transport property is studied in high-quality single crystals of BaFe2(As$_{1-x}$P$_{x})_{2}$. By substituting isoelectronic P for As, the spin-density-wave (SDW) state is suppressed and the dome-shaped superconducting phase ($T_{c} \quad \sim $ 31 K) appears. Near the SDW end point (x $\sim $ 0.3), we observe striking linear temperature ($T)$ dependence of resistivity in a wide $T$-range, and remarkable low-$T$ enhancement of Hall coefficient magnitude from the carrier number estimates. We also find that the magnetoresistance apparently violates the Kohler's rule and is well scaled by the Hall angle. These non-Fermi liquid transport anomalies cannot be attributed to the simple multiband effects. These results capture universal features of correlated electron systems in the presence of strong antiferromagnetic fluctuations. [1] S. Kasahara \textit{et al}., arXiv:0905.4427. [Preview Abstract] |
Monday, March 15, 2010 1:27PM - 1:39PM |
B40.00010: Evolution of the bulk properties, structure, magnetic order, and superconductivity with Ni doping in CaFe$_{2-x}$Ni$_{x}$As$_{2}$ Songxue Chi, Neeraj Kumar, Ying Chen, Kumari Gaurav Rana, A.K. Nigam, A. Thamizhavel, William Ratcliff, S.K. Dhar, Jeffrey W. Lynn Magnetization, susceptibility, specific heat, resistivity, neutron and x-ray diffraction have been used to characterize the properties of CaFe$_{2-x}$Ni$_{x}$As$_{2}$ as a function of Ni doping. The combined first-order structural and magnetic phase transition occur together in the undoped system, with a small decrease in the area of the $a-b$ plane along with an abrupt increase in the length of the $c$-axis in the orthorhombic phase. With increasing x the transition temperature decreases but remains sharp at modest dopings. At larger dopings the transition is more rounded, and decreases to zero for x$\approx $0.06 where superconductivity develops. The regime of superconductivity is quite restrictive, with a maximum T$_{C}$ of 15 K and an upper critical field H$_{C2}$=14 T. Superconductivity disappears in the overdoped region. [Preview Abstract] |
Monday, March 15, 2010 1:39PM - 1:51PM |
B40.00011: High Temperature Resistivity in the Sr-122 Iron Pnictides and in the Electron-Doped Cuprates Paul Bach, Shanta Saha, Kevin Kirshenbaum, Johnpierre Paglione, Richard Greene The electrical resistivity in the Sr-122 iron-pnictides and electron-doped cuprates were measured up to 800K. A resistivity saturation at the Mott-Ioffe-Regel limit was observed in the $SrFe_2As_2$ system, both in the parent compound and at several dopings, Ni=0.14, Ni=0.18, Co=0.3. Below this limit, but above the Debye temperature, the resistivity increases linearly. The electron-doped cuprates, PCCO and NCCO, were also measured at high temperatures. The resistivity does not saturate, showing a violation of the Mott-Ioffe-Regel limit consistent with other cuprate systems. This contrasts strongly with the 122's more typical metallic behavior. Supported by NSF grant DMR-0653535. [Preview Abstract] |
Monday, March 15, 2010 1:51PM - 2:03PM |
B40.00012: Upper Critical fields and Pauli Limiting Behavior in a FeSe$_{0.4}$Te$_{0.6}$ Single Crystal Seunghyun Khim, Jae Wook Kim, Eun Sang Choi, Yunkyu Bang, Minoru Nohara, Hidenori Takagi, Kee Hoon Kim We investigate temperature-dependence of the upper critical fields $\emph{H}_{c2}$($\emph{T}$) of a superconducting FeSe$_ {0.4}$Te$_{0.6}$ single crystal by measuring resistivity in static magnetic fields up to 45 T. $\emph{H}_{c2}$($\emph{T}$) along a planar $\emph{ab}$-direction, $\emph{H}_{c2}^{\emph{ab}} $($\emph{T}$), steeply increases near its superconducting transition temperature $\emph{T}_{c}$ $\sim$ 14.5 K, starts to saturate even around 10 K, and finally approaches $\emph{H}_{c2} ^{\emph{ab}}$(0) $\sim$ 48 T, a much smaller value than the expected orbital limiting field ($\sim$ 130 T), indicating the predominant Pauli limiting effect. Although $\emph{H}_{c2}^ {\emph{c}}$($\emph{T}$) increases with a smaller positive slope near $\emph{T}_{c}$, it shows a positive curvature at overall temperatures to reach $\emph{H}_{c2}^{\emph{c}}$(0) $\sim$ 48 T, suggesting the Pauli paramagnetic effect also exists even along the $\emph{c}$-direction. We include the spin-orbit coupling and the Pauli paramagnetic effect in the Werthamer- Helfand-Hohenberg (WHH) formula to explain the shape of $\emph {H}_{c2}$($\emph{T}$) for both directions and discuss enhanced local magnetism resulting from the excess iron or Se(Te) vacancies as a possible origin for the persistent Pauli limiting behavior. [Preview Abstract] |
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