Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Z40: Superconductivity: Spectroscopy (Neutron, Optical and others) |
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Sponsoring Units: DCMP Chair: Wei Bao, Renmin University of China Room: F151 |
Friday, March 19, 2010 11:15AM - 11:27AM |
Z40.00001: Evolving Picture of Striped Superconductivity in La$_{2-x}$Ba$_x$CuO$_4$ John Tranquada, Genda Gu, Chris Homes, Markus Huecker, Qiang Li, Jinsheng Wen, Guangyong Xu, Zhijun Xu We have previously presented experimental evidence for two-dimensional superconductivity in La$_{1.875}$Ba$_{0.125}$CuO$_4$ coexisting with charge and spin stripe order for $T < 40$ K. A pair-density-wave (PDW) state has been proposed to explain the dynamical layer decoupling; however, recent photoemission measurements indicate that a $d$-wave gap develops on the nodal arc in the same temperature range. We show that our various experimental results are consistent with the onset of PDW correlations together with the charge-stripe order at 53 K, followed by the development of uniform $d$-wave superconductivity. We can rule out layer decoupling due to a charge-density-wave gap. [Preview Abstract] |
Friday, March 19, 2010 11:27AM - 11:39AM |
Z40.00002: Effect of covalent bonding on magnetism and the missing neutron intensity in cuprates Igor Zaliznyak, Andrew Walters, Toby Perring, Andrei Savici, Genda Gu, Chi-Cheng Lee, Wei Ku, Jean-Sebastien Caux We report a detailed survey of magnetic excitations in the one- dimensional cuprate Sr2CuO3 using inelastic neutron scattering (INS). We show that although the overall shape of the experimental dynamical spin structure factor is well described by the exact theory [1] of the model spin-1/2 nearest-neighbour Heisenberg Hamiltonian typically used for cuprates, the magnetic intensity is strongly suppressed, by factor 2.5-3, compared to the ionic spin model. We further show that this dramatic modification results from strong hybridization of Cu 3d states with O p states, showing that the ionic picture of localized 3d Heisenberg spin magnetism is markedly inadequate. Our findings provide natural explanation for the puzzle of the missing INS magnetic intensity in cuprates and have profound implications for understanding current and future experimental data on these materials [2]. We observe no corrections to spin excitations spectral weight resulting from electron itineracy. [1] J.-S. Caux and R. Hagemans, J. Stat. Mech., P12013 (2006). [2] A. Walters, T. Perring, A. Savici, G. Gu, C. Lee, W. Ku, J.-S. Caux and I. A. Zaliznyak, Nature Physics 5 (2009). [Preview Abstract] |
Friday, March 19, 2010 11:39AM - 11:51AM |
Z40.00003: Bosonic spectral density of optimally and overdoped LSCO superconductors from optical spectroscopy Greg Egan, Jungseek Hwang, Sarah Purdy, Jules Carbotte, Thomas Timusk, Ewald Schachinger Optical spectroscopy on single crystals of optimally doped La$_{2- x}$Sr$_{x}$CuO$_{4}$ (x=0.17) show two bosonic peaks at ~50 meV and ~18 meV at low temperatures (30K) as reported by Hwang et al[1]. The bosonic spectrum is acquired through the Eliashberg formalism by inverting the measured optical spectra, and shows a remarkable similarity to the spin excitation spectrum achieved through inelastic neutron scattering results. The optical study is extended into the overdoped region (x=0.22) for which detailed neutron scattering results suggest a suppression of the strong 50 meV response and a characteristic shift from 18 meV to 10 meV of the low energy response. [1] J. Hwang, E. Schachinger, J.P. Carbotte, F. Gao, D.B. Tanner, T. Timusk, Phys. Rev. Letters 100, 137005 (2008) [Preview Abstract] |
Friday, March 19, 2010 11:51AM - 12:03PM |
Z40.00004: Scaling analysis of the static and dynamic critical exponents in Pr$_{2-x}$Ce$_x$CuO$_4$ films as a function of doping R.A. Isaacs, M.C. Sullivan, M.F. Salvaggio, J. Sousa, C.G. Stathis, J.B. Olson We investigate the static and dynamic critical exponents of the electron-doped superconductor Pr$_{2-x}$Ce$_x$CuO$_4$. Our results are based on current vs.\ voltage measurements in zero-field of the normal-superconducting phase transition in Pr$_{2-x}$Ce$_x$CuO$_4$ films as a function of doping. We find that these materials posses an unusually small critical regime ($\sim$25mK) that gives rise to mean-field behavior at the phase transitions and a static critical exponent of about $\nu\sim$0.5 for all dopings. This is quite unexpected when compared to the critical behavior seen in well-known hole-doped superconductor YBa$_2$Cu$_3$O$_7$, where $\nu\sim$2/3. In addition, mean-field behavior is also exhibited in the dynamic critical exponent ($z$). We find that Pr$_{2-x}$Ce$_x$CuO$_4$ behaves not like other cuprate superconductors, but similarly to conventional superconductors in this regard. Only as transition width decreases to zero does the dynamic critical exponent ($z$) approach the value found in YBa$_2$Cu$_3$O$_7$. [Preview Abstract] |
Friday, March 19, 2010 12:03PM - 12:15PM |
Z40.00005: Coexistence of weak ferromagnetism and superconductivity in rutheno-cuprate RuSr$_2$Eu$_{1.5}$Ce$_{0.5}$Cu$_2$O$_{10}$ Daniel Haskel, Narcizo M. Souza-Neto, Jonathan C. Lang, Omar Chmaissem, Bogdan Dabrowski, Israel Felner We address the question of possible coexistence between weak ferromagnetism (W-FM) and superconductivity (SC) in the Ru-1222 rutheno-cuprate layered structure using element-specific x-ray magnetic circular dichroism (XMCD) and x-ray absorption fine structure (XAFS) measurements. XMCD probes Ru magnetization independently from the paramagnetic contributions of rare-earth ions and XAFS is ideally suited for detection of nano-sized impurities that may go undetected in diffraction measurements. We report the presence of a significant zero-field FM component (0.21 $\mu\rm{_B}$/Ru) associated with Ru ions in the Ru-1222 lattice. The results, together with bulk susceptibility and resistivity measurements, imply by necessity coexistence of W-FM and SC at the atomic level in this rutheno-cuprate structure [see N. M. Souza-Neto {\it et al.}, Phys. Rev. B {\bf 80}, R140414 (2009).] [Preview Abstract] |
Friday, March 19, 2010 12:15PM - 12:27PM |
Z40.00006: Quasiparticle scattering from a double vortex scatterer in d-wave superconductors Sriram Ganeshan, Manas Kulkarni, Adam C. Durst The low energy quasiparticle excitations of a d-wave superconductor are massless Dirac fermions. In the presence of a magnetic field, the scattering of quasiparticles from vortices receives both a superflow contribution, due to interaction with the superflow circulating about each vortex, as well as a Berry phase contribution, due to the Berry phase acquired upon circling a vortex. Calculating the cross section for quasiparticle scattering from a double vortex provides a clean way of isolating and studying the two effects. We do so by making use of elliptical coordinates, a natural setting for studying this two-center problem. With proper gauge choice, the Berry phase contribution takes the form of a branch cut between vortex centers, providing a boundary condition for the spinor wave function across the line segment joining the foci of the elliptical coordinate system. We solve the quantum scattering of Dirac quasiparticles in elliptical coordinates. Our approach is to separate the free Dirac equation in elliptical coordinates. The separated angular and radial functions turn out to be the solutions of angular and modified Whittaker-Hill's equations. We summarize the technique to expand incident plane wave spinor in terms of Whittaker-Hill functions. We also present the asymptotic form of the separated solutions in order to setup an analytical formula for differential cross section. [Preview Abstract] |
Friday, March 19, 2010 12:27PM - 12:39PM |
Z40.00007: Broken rotational symmetry in the pseudogap phase of a high-Tc superconductor J. Chang, R. Daou, D. LeBoeuf, O. Cyr-Choiniere, F. Laliberte, N. Doiron-Leyraud, B.J. Ramshaw, R. Liang, D.A. Bonn, W.N. Hardy, L. Taillefer The nature of the pseudogap phase is a central problem in the quest to understand high-$T_c$ cuprate superconductors. A fundamental question is what symmetries are broken when that phase sets in below a temperature $T^*$. Here we report the observation of a large in-plane anisotropy of the Nernst effect in YBa$_2$Cu$_3$O$_y$ that sets in precisely at $T^*$, throughout the doping phase diagram [1]. We show that the CuO chains of the orthorhombic lattice are not responsible for this anisotropy, which is therefore an intrinsic property of the CuO$_2$ planes. We conclude that the pseudogap phase is an electronic state which strongly breaks four-fold rotational symmetry.\\[4pt] [1] R. Daou et al., arXiv:0909.4430 [Preview Abstract] |
Friday, March 19, 2010 12:39PM - 12:51PM |
Z40.00008: Constraints on Models of Electrical Transport in Optimally Doped La$_{\rm 2-x}$Sr$_{\rm x}$CuO$_{\rm 4}$ from Precise Measurements of Radiation-Induced Defect Resistance Jeffrey Clayhold, Oshri Pelleg, David Ingram, Anthony Bollinger, Gennady Logvenov, David Rench, Bryan Kerns, Michael Schroer, Robert Sundling, Ivan Bozovic Recent studies of normal-state magnetotransport in overdoped cuprate superconductors have shed much light on charge carrier transport, showing that both linear T and T$^2$ scattering rates are distributed around the Fermi surface. Unfortunately, the most discerning magnetotransport probes are not easily applied for the most interesting, optimally-doped cuprates. We have been able to characterize anisotropic scattering in La$_{\rm 1.83}$Sr$_{\rm 0.17}$CuO$_{\rm 4}$ by using a mostly overlooked but powerful resource---measuring the temperature dependence of the defect scattering resistance. When different regions of the Fermi surface contribute to conduction with different temperature dependences, then the gradual degradation of each contribution via added scattering alters the balance in a characteristic way that reveals much about how transport varies around the Fermi surface. Careful new measurements and a new analysis show how both T and T$^2$ scattering rates coexist as separate parallel conductance channels in La$_{\rm 1.83}$Sr$_{\rm 0.17}$CuO$_{\rm 4}$. [Preview Abstract] |
Friday, March 19, 2010 12:51PM - 1:03PM |
Z40.00009: Probing magnons with RIXS Lucas Ament, Giacomo Ghiringhelli, Marco Moretti Sala, Lucio Braicovich, Jeroen van den Brink Resonant Inelastic X-ray Scattering (RIXS) at the copper L and M edge can probe single spin-flips, which makes it possible to probe the dispersion of magnetic excitations (for instance magnons) of cuprates such as the high Tc superconductors [1]. The cross section factors into a local, atomic spin flip scattering amplitude and a momentum dependent factor describing the final state excitation. Recently, the single magnon dispersion has been measured and found to coincide with earlier neutron measurements [2]. For the cuprates, these results put RIXS as a technique on the same footing as neutron scattering, opening a new window for experiments on this class of materials. \newline \newline [1] L.J.P. Ament, G. Ghiringhelli, M. Moretti Sala, L. Braicovich, and J. van den Brink, PRL {\bf 103}, 117003 (2009) \newline [2] L. Braicovich, J. van den Brink, V. Bisogni, M. Moretti Sala, L.J.P. Ament, N.B. Brookes, G.M. De Luca, M. Salluzzo, T. Schmitt, and G. Ghiringhelli, arXiv:0911.0621 [Preview Abstract] |
Friday, March 19, 2010 1:03PM - 1:15PM |
Z40.00010: Direct observation of bulk Fermi surface at higher Brillouin zones in a heavily hole-doped cuprate W. Al-Sawai, Y. Sakurai, M. Itou, B. Barbiellini, P.E. Mijnarends, R.S. Markiewicz, S. Kaprzyk, J.-M. Gillet, S. Wakimoto, M. Fujita, S. Basak, H. Lin, A. Bansil, K. Yamada We have observed the bulk Fermi surface (FS) in an overdoped ($x$=0.3) single crystal of La$_{2-x}$Sr$_x$CuO$_4$ by using Compton scattering. A 2-D momentum density reconstruction [1] from measured Compton profiles, yields a clear FS signature in a higher Brillouin zone centered at p=(1.5,1.5) a.u. The quantitative agreement with density functional theory (DFT) calculations [2] and momentum density experiment suggests that Fermi-liquid physics is restored in the overdoped regime. We have also measured the 2-D angular correlation of positron annihilation radiation (2D-ACAR) [3] and noticed a similar quantitative agreement with the DFT simulations. However, 2D-ACAR does not give a clear signature of the FS in the extended momentum space in both theory and experiment. Work supported in part by the US DOE.\\ \mbox{[1]} Y. Tanaka \textit{et al.}, Phys. Rev. B {\bf 63}, 045120 (2001).\\ \mbox{[2]} S. Sahrakorpi \textit{et al.}, Phys. Rev. Lett. {\bf 95}, 157601 (2005).\\ \mbox{[3]} L. C. Smedskjaer \textit{et al.}, J. Phys. Chem. Solids {\bf 52}, 1541 (1991). [Preview Abstract] |
Friday, March 19, 2010 1:15PM - 1:27PM |
Z40.00011: Dynamical structure factor computations in extended momentum space in electron doped cuprates Yung Jui Wang, B. Barbiellini, Hsin Lin, Tanmoy Das, Susmita Basak, P. E. Mijnarends, S. Kaprzyk, R. S. Markiewicz , A. Bansil We report first principles computations of the dynamical structure factor $S(q,\omega)$ in the electron doped cuprates Nd$_{2-x}$Ce$_{x}$CuO$_{2}$ as a function of energy $\omega$ and momentum $q$ extended over several Brillouin zones. We show the efficacy of obtaining $S(q,\omega)$ through the use of simple products of real space Green functions and fast Fourier transform (FFT). We also calculate the susceptibility $\chi(q,\omega)$ efficiently by recalling that $S(q,\omega)$ is proportional to the imaginary part of the susceptibility $\chi(q,\omega)$. The present work is useful in going beyond the standard LDA-based modeling of various highly resolved spectroscopies.[1-4] We will provide some illustrative examples. Work supported by the US DOE.\\ \mbox{[1]} R. S. Markiewicz \textit{et al.}, Phys. Rev. Lett. {\bf 96}, 107005 (2006).\\ \mbox{[2]} S. Sahrakorpi \textit{et al.}, Phys. Rev. Lett. {\bf 95}, 157601 (2005).\\ \mbox{[3]} G. Stutz \textit{et al.}, Phys. Rev. B {\bf 60}, 7099 (1999).\\ \mbox{[4]} J. Nieminen \textit{et al.}, Phys. Rev. Lett. {\bf 102}, 037001 (2009). [Preview Abstract] |
Friday, March 19, 2010 1:27PM - 1:39PM |
Z40.00012: Fermi Liquid Description of X-ray Absorption Spectra in Overdoped LSCO Towfiq Ahmed, John J. Rehr, Joshua J. Kas, Tanmoy Das, Hsin Lin, Robert S. Markiewicz, Bernardo Barbiellini-Amidei, Arun Bansil We show that a paramagnetic self-energy correction [1] to the real-space Green's function code FEFF9 [2] can provide a good description of the x-ray absorption spectra (XAS) of cuprate system such as La$_{\rm (2-x)}$Sr$_{\rm (x)}$CuO$_{\rm 4}$ (LSCO). This self energy includes coupling to both charge and magnetic excitations. We also find good agreement with recent XAS results of Peet et al. [3] in the over-doped regime of LSCO. We have also investigated various prescriptions for including core-hole effects. We infer that at low doping, the system behaves as an anti-ferromagnetic insulator, while Fermi liquid physics is recovered at high doping. \\ \mbox{[1]}Tanmoy Das, R.S. Markiewicz, and A. Bansil, Phys.Rev. B {\bf 77}, 134516 (2008). \\ \mbox{[2]} J. J. Rehr et al., Comptes Rendus Physique {\bf 10}, 548 (2009).\\ \mbox{[3]} D.C. Peets \textit{et al.}, Phys. Rev. Lett. {\bf 103}, 087402 (2009). [Preview Abstract] |
Friday, March 19, 2010 1:39PM - 1:51PM |
Z40.00013: Quantitative determination of penetration depth using magnetic force microscopy Joshua Thibodaux, Evgueni Nazaretski, Leonardo Civale, Joe Thompson, Roman Movshovich, Ilya Vekhter Extracting quantitative information from magnetic force microscopy has long been considered a difficult problem. We present a method to extract a numerical value of the penetration depth utilizing detailed knowledge of the MFM tip properties. Modeling the vortex field as that of a magnetic monopole we use the experimental data on a Nb film to find a penetration depth that is in good agreement with SQUID magnetometer measurements. We discuss the influence of tip geometry on the extracted values of the penetration depth and explore the differences between the simple model of the vortex field and a detailed calculation in the London model. [Preview Abstract] |
Friday, March 19, 2010 1:51PM - 2:03PM |
Z40.00014: Fermi surfaces and quantum oscillations in underdoped high-T$_{c}$ superconductors YBa$_{2}$Cu$_{3}$O$_{6.5 }$and YBa$_{2}$Cu$_{4}$O$_{8}$ Hyungju Oh, Hyoung Joon Choi, Steven G. Louie, Marvin L. Cohen We study the underdoped high-T$_{c}$ superconductors YBa$_{2}$Cu$_{3}$O$_{6.5}$ and YBa$_{2}$Cu$_{4}$O$_{8}$ using first-principles pseudopotential methods with additional Coulomb interactions at Cu atoms and obtain Fermi-surface pocket areas in close agreement with measured Shubnikov-de Haas and de Haas-van Alphen oscillations. With antiferromagnetic order in CuO$_{2}$ planes, stable in the calculations, small hole pockets are formed near so-called Fermi-arc positions, reproducing the low-frequency oscillations. A large electron pocket, necessary for the negative Hall coefficient, is formed in YBa$_{2}$Cu$_{3}$O$_{6.5}$, giving rise to the high-frequency oscillation as well. Effective masses and specific heats are also calculated and compared with measurements. Our results highlight the crucial role of magnetic order in the electronic structure of underdoped high-T$_{c}$ superconductors. This work was supported by the KRF Grant No. KRF-2007-314-C00075, the KOSEF Grant No. R01-2007-000-20922-0, NSF Grant No. DMR07-05941, and DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by KISTI Supercomputing Center (Project No. KSC-2008-S02-0004), NSF through TeraGrid resources, and DOE NERSC. [Preview Abstract] |
Friday, March 19, 2010 2:03PM - 2:15PM |
Z40.00015: Temperature-dependent spectral weight transfer in YBa$_2$Cu$_3$O$_x$ probed by x-ray absorption spectroscopy J.-Y. Lin The x-ray absorption spectroscopy was utilized to critically examine the temperature dependency of the spectral weight in YBa$_2$Cu$_3$O$_x$. Large excess spectral weight for the Zhang- Rice singlet due to dynamics of holes is found with its doping dependence showing similar doom-like shape as that for $Tc$. Furthermore, appreciable spectral weight transfer from the upper Hubbard band to Zhang-Rice singlet was observed as the temperature acrosses the onset temperature for the pseudogap. The observed spectral weight transfer follows the change of the pseudogap, indicating a strong link between pseudogap and the upper Hubbard band. [Preview Abstract] |
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