Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session D39: Spin Properties of Superconductors |
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Sponsoring Units: DCMP Chair: Jeff Lynn, National Institute of Standards and Technology Room: Baltimore Convention Center 342 |
Monday, March 13, 2006 2:30PM - 2:42PM |
D39.00001: Electron-phonon coupling associated with charge-stripe order in cuprate superconductors John Tranquada, D. Reznik, L. Pintschovius, M. Ito, S. Iikubo, M. Sato, M. Fujita, K. Yamada, G. D. Gu We have used inelastic neutron scattering to study the Cu-O bond-stretching phonon in La$_{1.875}$Ba$_{0.125}$CuO$_{4}$ and La$_{1.48}$Nd$_{0.4}$Sr$_{0.12}$CuO$_{4}$, two cuprate compounds that exhibit charge-stripe order. This is the phonon mode that one expects to be most sensitive to spatial inhomogeneity in the electronic structure of the CuO$_{2}$ planes. Besides the cosine-like downward dispersion of the mode from zone center to zone boundary, we observe a dip in the dispersion and a very large energy width ($>$ 10 meV) at \textbf{q} = \textbf{a}*/4. The dip and width gradually become smaller with increasing temperature. These evidences of a strong electron-phonon coupling (the dispersion dip and large energy width) have not been predicted by any conventional calculations. The nature of the connection with charge-stripe order will be discussed. [Preview Abstract] |
Monday, March 13, 2006 2:42PM - 2:54PM |
D39.00002: Magnetic Neutron Scattering Study of Nd$_{1.85}$Ce$_{0.15}$Cu$_{1-y}$Ni$_{y}$O$_{4}$ Single Crystals Inna Vishik, Guichuan Yu, Eugene Motoyama, Owen Vajk, Martin Greven In order to arrive at a deeper understanding of the interplay between superconductivity and magnetism in the high-temperature superconductors, it is of interest to study the effects of impurity-doping on the copper site. A large body of work along these lines exists for hole-doped materials, yet relatively little is known about the effects of such impurities on the prototypical electron-doped material (Nd,Ce)$_{2}$CuO$_{4}$. In previous work, paramagnetic dopants (Ni, Fe) were shown to lower T$_{c}$ much more abruptly than non-magnetic ones (Zn). We grew large single crystals of Nd$_{1.85}$Ce$_{0.15}$Cu$_{1-y}$Ni$_{y}$O$_{4}$ using the traveling-solvent floating-zone technique and characterized our samples using SQUID magnetometry and DC transport measurements. Here we report on neutron scattering results for the spin correlations as a function of nickel concentration and temperature for superconducting (y $<$ 0.01) and non-superconducing (y$>$ 0.01) compositions. [Preview Abstract] |
Monday, March 13, 2006 2:54PM - 3:06PM |
D39.00003: Scattering Studies of the High T$_c$ Superconductor La$_{2-x}$Ba$_{x}$CuO$_{4}$ Y. Zhao, S. R. Dunsiger, B. D. Gaulin, H. A. Dabkowska, Z. Yamani, W. J. L. Buyers The interplay between superconductivity, magnetism and crystal structure is a central issue in the study of the high T$_c$ cuprates. The first to be discovered, the Bednorz-M\"{u}ller materials have been much less extensively studied due to the difficulty of growing large single crystals. Using floating zone image furnace techniques, we have recently successfully grown La$_{2-x}$Ba$_{x}$CuO$_{4}$ (x$\sim$0.095 and 0.08) single crystals on the underdoped side of the well known 1/8 anomaly. X-ray studies show a sequence of crystal structures with temperature, while incommensurate elastic peaks associated with the low temperature tetragonal phase are observed using neutron diffraction. This signature of static spin stripe order persists into the superconducting state. We discuss the relationship between the low temperature spin and lattice degrees of freedom, as well as their sensitivity to doping level. [Preview Abstract] |
Monday, March 13, 2006 3:06PM - 3:18PM |
D39.00004: Electronic inhomogeneities in superconducting YBa$_{2}$Cu$_{3}$O$_{6+x}$ Ferenc Stercel, Jae-Ho Chung, Takeshi Egami, Masatoshi Arai, Tetsuya Yokoo, Hyungje Woo, Mohana Yethiraj, Herb A. Mook, Chris D. Frost, Fatih Dogan There has been an increasing amount of experimental evidence for the presence of local electronic inhomogeneities in superconducting cuprates. Inelastic pulsed neutron scattering measurements on YBa$_{2}$Cu$_{3}$O$_{6+x }$single crystals with different oxygen concentrations show that the zone boundary softening of the in-plane LO Cu-O bond stretching mode is the same for all doping levels. In addition, the spectral weight of the softened mode increases with increasing doping. This indicates that there is a microscopic electronic phase separation in superconducting YBa$_{2}$Cu$_{3}$O$_{6+x}$. Furthermore, triple axis inelastic neutron scattering measurements on the underdoped YBa$_{2}$Cu$_{3}$O$_{6.6}$ performed at different temperatures revealed that a new local mode appears at 65 meV at higher temperatures (200 K and above). It might indicate the presence of polarons. [Preview Abstract] |
Monday, March 13, 2006 3:18PM - 3:30PM |
D39.00005: Spin Excitations of overdoped La$_{2-x}$Sr$_{x}$CuO$_{4}$ S. Wakimoto, R.J. Birgeneau, C.D. Frost, A. Kagedan, H.K. Kim, I. Swainson, J.M. Tranquada, K. Yamada, H. Zhang Spin excitations of LSCO in the overdoped regime have been studied by neutron scattering. Incommensurate excitations around 6 meV which are clearly observed in the $x=0.25$ sample decrease with $T_c$ as doping increases, and finally, become unobservable at $x=0.30$ coincidentally with the disappearance of bulk superconductivity. High-energy measurements performed at the MAPS spectrometer show remarkably weakened magnetic excitations of the overdoped samples also in the high energy region. These observations are apparently consistent with a microscopic phase separation of the overdoped samples into the superconducting and Fermi liquid phases based on muSR results. in contrast, magnetization measurements of overdoped LSCO with and without Zn impurities have revealed that the superconductivity vanishes in the overdoped regime as a result of a competition between the superconductivity and paramagnetism which is induced even in the Zn-free overdoped LSCO. [Preview Abstract] |
Monday, March 13, 2006 3:30PM - 3:42PM |
D39.00006: Search for Magnetic Order in Superconducting RuSr$_{2}$Eu$_{1.2}$Ce$_{0.8}$Cu$_{2}$O$_{10}$ J. W. Lynn, Y. Chen, S.K. Goh, G.V.M. Williams Neutron diffraction, polarized neutron transmission, and small angle neutron scattering have been used to investigate the nature of the magnetic order in the titled compound. The sample was made with the Eu-153 (98.8\%) isotope to reduce the high neutron absorption for this element. At low T a single magnetic peak is clearly observed. A sharp spin reorientation transition (SRT) is observed around 35 K, close to the superconducting transition temperature (Tc~40K). Between the SRT and the Neel temperature of 59 K, additional magnetic reflections are observed. However, none of these can be simply indexed on the chemical unit cell, either as commensurate peaks or simple incommensurate magnetism, and the paucity of reflections at low T compels the conclusion that these arise from an impurity phase. X-ray and neutron diffraction both show that the sample does not appear to contain significant impurity phases. However, the impurity peaks exhibit strong preferred orientation, while the primary phase does not. We have been unable to observe any magnetic order that can be identified with the ruthenate-cuprate system. Additional field-dependent results will be discussed. [Preview Abstract] |
Monday, March 13, 2006 3:42PM - 3:54PM |
D39.00007: High-Energy Excitations near the boundary to antiferromagnetism-YBCO6.35 C. Stock, R.A. Cowley, W.J.L. Buyers, C.L. Broholm, R. Coldea, C.D. Frost, R.J. Birgeneau, R. Liang, D. Bonn, W.N. Hardy The high-energy magnetic excitations in the cuprate superconductors have attracted considerable interest recently. We investigate magnetic excitations over the entire energy range in the heavily underdoped YBCO6.35 superconductor with a Tc=18 K. The spin response below 25 meV energy transfers is broad and has been discussed previously. The magnetic response above 25 meV is very similar to the parent insulators with similar spectral weight and spin-wave velocity. The excitations near the zone boundaries are however, much broader in energy than for the parent insulator. The onset of damping coincides approximately with the gap determined from transport measurements. This indicates that a new decay channel for spin waves becomes available above the pseudo-gap. [Preview Abstract] |
Monday, March 13, 2006 3:54PM - 4:06PM |
D39.00008: Spin susceptibility of underdoped cuprates: the case of Ortho-II YBa$_2$Cu$_3$O$_{6.5}$ Elena Bascones, T. Maurice Rice Recent inelastic neutron scattering measurements found that the spin susceptibility of detwinned and highly ordered ortho-II YBa$_2$Cu$_3$O$_{6.5}$ exhibits, in both the normal and superconducting states, one-dimensional incommensurate modulations at low energies which were interpreted as a signature of dynamic stripes. We propose an alternative model based on quasiparticle transitions between the arcs of a truncated Fermi surface. Such transitions are resonantly enhanced by scattering to the triplet spin resonance. We show that the anisotropy in the experimental spin response is consistent with this model if the gap at the saddle points is anisotropic. [Preview Abstract] |
Monday, March 13, 2006 4:06PM - 4:18PM |
D39.00009: Effect of Charge Inhomogeneity on the Diagonal Incommensurate Spin Correlations in La$_{2-x}$Sr$_{x}$CuO$_{4}$ Masaaki Matsuda, Masaki Fujita, Kazuyoshi Yamada Neutron-scattering experiments are performed on Zn and Ni doped La$_{1.95}$Sr$_{0.05}$CuO$_{4}$ to study the impurity effect on the diagonal incommensurate spin correlations. Zn doping reduces the incommensurability and enhances the correlation length just slightly. On the other hand, Ni doping quickly destroys the incommensurability and restores N¥'{e}el ordering, indicating a strong effect on hole localization. This suggests that Ni and hole form a strongly bound state with the Zhang-Rice character, in which effective valence and spin number are trivalent and 1/2, respectively. Although it is expected that doped Ni with effective spin 1/2 does not disturb the magnetic interactions so much, the magnetic correlations are disordered considerably. This suggests that the charge inhomogeneity, caused by the random distribution of effectively trivalent Ni, disturbs the stripe formation and the magnetic correlations become disordered. This result supports the diagonal stripe state and probably rules out the spiral state, caused by the magnetic frustration, in lightly-doped La$_{2-x}$Sr$_{x}$CuO$_{4}$. [Preview Abstract] |
Monday, March 13, 2006 4:18PM - 4:30PM |
D39.00010: Magnetic Excitations of Stripes Near a Quantum Critical Point and Checkerboards David K. Campbell, Daoxin Yao, Erica W. Carlson Competing tendencies in electronic systems with strong correlations can lead to spontaneous nanoscale structure, pattern formation, and even long-range spatial order.~ There has been continued interest in various charge and spin spatial order, including ``stripe" and ``checkerboard" phases. We explore the magnetic excitations of stripe and checkerboard phases within a semiclassical spin wave approximation.~ We show that simple checkerboard patterns are incompatible with recent neutron scattering experiments, while stripes near a quantum critical point (i.e. with weak coupling across the domain walls)~exhibit much of the~ behavior seen in recent neutron scattering experiments on high temperature superconductors. At low energies, the spin wave cones of weakly coupled stripes have weight strongly peaked on the inner branches.~ As energy is increased, a saddlepoint produces a resonance peak, followed by a square-shaped continuum rotated 45 degrees from the low energy peak direction. We discuss the connection to recent high energy neutron scattering data on the cuprates, as well as the relation to quantum spin fluctations. [Preview Abstract] |
Monday, March 13, 2006 4:30PM - 4:42PM |
D39.00011: Effect of spin-orbit scattering on the observed time-reversal violating phase in the Pseudogap phase of the Cuprates Vivek Aji, Chandra Varma Fauque et al. [1] have recently reported observing the predicted symmetry breaking [2] in the Pseudogap region in the phase-diagram of the Cuprates, which had also been earlier inferred from dichroism in ARPES. Following Wu et al. [3], we study the effects of spin-orbit scattering inthe observed symmetry breaking. We study the following issues: spin-current, accompanying orbital currents, symmetry of any accompanying spin-order, and the effect of an external magnetic-field on the ordered state. 1. Fauque et al., arXiv.org/cond-mat/0509210; 2. M.E. Simon and C.M.Varma, Phys.Rev. Lett. 89, 247003 (2002) 3.Wu et al., arXiv.org/cond-mat/0505544 [Preview Abstract] |
Monday, March 13, 2006 4:42PM - 4:54PM |
D39.00012: $^{17}$O and $^{139}$La NMR in a single crystal La$_{2-x}$Ba$_{x}$CuO$_{4}$, $x=1/8$ Ben-Li Young, N. J. Curro, J. Haase, H.-J. Grafe, B. B{\"{u}}chner, M. H{\"{u}}cker, G. D. Gu We have performed $^{17}$O and $^{139}$La nuclear magnetic resonance (NMR) in a single crystal of La$_{2-x}$Ba$_{x}$CuO$_ {4}$ with $x=1/8$, in order to investigate how the static spin and charge structures, as revealed by neutron scattering, influence the NMR spectrum. We measured the NMR intensity of the $^{17}$O and $^{139}$La nuclei, as well as the $^{17}$O nuclear quadrupole resonance frequency ($\nu_{Q}$) at several different temperatures. We will discuss possible correlation between the $^{17}$O signal intensity and $\nu_{Q}$ as a function of temperature due to the stripe phase. [Preview Abstract] |
Monday, March 13, 2006 4:54PM - 5:06PM |
D39.00013: NMR studies of Pr$_{2-x}$Ce$_{x}$CuO$_{4-y}$ ($\it{x}$ = 0.15 and 0.17) at high magnetic field Guoqing Wu, S.E. Brown, W.G. Clark, R.L. Greene, H. Balci, P. Kuhns, A.P. Reyes, W.G. Moulton Recent charge and thermal transport measurements on the electron- doped high-T$_{c}$ superconductor Pr$_{2-x}$Ce$_{x}$CuO$_{4-y}$ (PCCO) show unusual behavior in the superconducting dome at the doping level going from $\it{x}$ = 0.15 (optimally doped) to 0.17 (overdoped), such as quantum phase transition and electron paring symmetry changes, suggesting a possible connection between the superconductivity and other competing phases like antiferromagnetism. We report the $^{63,65}$Cu-NMR spectrum in PCCO single crystals with $\it{x}$ = 0.17 in a high magnetic field B$_{0}$, and contrast their properties with those of $\it {x}$ = 0.15. The temperature dependence of the $^{63,65}$Cu-NMR Knight shift is dominated by the negative isotropic hyperfine coupling to the field-induced Pr$^{3+}$ ion moment, and changes little between $\it{x}$ = 0.15 and 0.17. The $^{63,65}$Cu-NMR linewidths are propotional to the applied magnetic field B$_{0} $, but affected by the doping, indicating the existence of other sources besides the Pr$^{3+}$ ion moment that contributes to the static local field distribution at the Cu nuclei. The work at UCLA is supported at UCLA by NSF Grants DMR-0334869 (WGC) and 0203806 (SEB). [Preview Abstract] |
Monday, March 13, 2006 5:06PM - 5:18PM |
D39.00014: Impurity effect on nuclear magnetic relaxation due to orbital hyperfine interaction A. Knigavko, B. Mitrovic, K. V. Samokhin We show that the nuclear magnetic relaxation rate $1/T_1$ due to the coupling of nuclear spin to the orbital moment of itinerant electrons is sensitive to impurity scattering in both normal and superconducting states. In the clean case $1/T_1$ diverges because of the contribution from distant currents, while in the dirty case its magnitude is controlled by the parameter $k_F l$, where $l$ is the electron mean free path. In the superconducting state temperature dependence of $1/T_1$ becomes significant. [Preview Abstract] |
Monday, March 13, 2006 5:18PM - 5:30PM |
D39.00015: On electron-hole symmetry and phase separation in some electron doped cuprates Lev Gor`kov, Gregory Teitel`baum Analyzing the experimental NMR data for electron-doped cuprates, we concluded that the Coulomb effects caused by doping lead to dynamical spatial phase separation that contributes to the nuclear spin relaxation. Remarkable, the ``infinite-layer'' Sr$_{0.9}$La$_{0.1}$CuO$_{4}$ reveals unexpected electron-hole symmetry. Its $^{63}$Cu nuclear spin relaxation rate is the sum of a constant and the temperature dependent components, moreover, the latter turns out to be identical to the $1/63T_{1}(T)$-behavior in the stoichiometric YBa$_{2}$Cu$_{4}$O$_{8}$. Connection to fluctuation of a magnetic sub-phase is discussed. [Preview Abstract] |
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