Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session J23: Focus Session: Cuprates and Nickelates |
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Sponsoring Units: DMP GMAG Chair: John Tranquada, Brookhaven National Laboratory Room: Morial Convention Center 215 |
Tuesday, March 11, 2008 11:15AM - 11:51AM |
J23.00001: Unidirectional charge modulations in underdoped cuprates observed with STM Invited Speaker: |
Tuesday, March 11, 2008 11:51AM - 12:03PM |
J23.00002: Phase Separation and Magnetism in High Tc Superconductors Samuel Emery, Barrett Wells, Hashini Mohottala, Joseph Budnick, William Hines, Linda Udby, Kim Lefmann, Neils Hessel Andersen, Christof Niedermayer, Niels Christensen, Jeffrey Lynn, Fangcheng Chou Previous work by our group has determined that the low temperature phase diagram of super-oxygenated, La$_{2}$CuO$_{4}$ consists of only a few line phases that are either superconducting (SC) or magnetic. Samples with doping levels between the stable phases will segregate into separate domains; this raises the question as to the nature of the interaction between SC and magnetic domains. We have begun a neutron scattering study of the magnetic behavior of two such crystals. The oxidation states vary such that in one sample we have a phase separation between a low Tc (30K) SC phase and a striped magnetic phase, while the other features a high Tc (40K) SC phase and striped magnetic phase. Elastic neutron scattering reveals little field dependence of the magnetic peaks in the former, but in the latter we see an enhancement of the magnetic intensity. We also are deriving a method for separating contributions to the inelastic magnetic scattering by the SC and magnetic phases. [Preview Abstract] |
Tuesday, March 11, 2008 12:03PM - 12:15PM |
J23.00003: Spin order and dynamics in a low doped nickelate Andrei Savici, Igor Zaliznyak, Genda Gu, Vasile Garlea Due to their similarities with high-Tc cuprates, doped 214 layered nickelates attract significant interest. We have recently performed elastic and inelastic neutron scattering experiments studying the low-Sr-doped material La$_1.85$Sr$_0.15$NiO$_{4+\delta}$. This sample has nominal hole concentration similar to that in optimally doped cuprate supeconductors. We observe static spin and charge ordering patterns and dynamic spin correlations, which we will compare to those arising from one dimensional physics expected in the stripe picture. [Preview Abstract] |
Tuesday, March 11, 2008 12:15PM - 12:27PM |
J23.00004: Detection of the Spin Reorientation and Glassy Dynamics in La$_{1.55}$Sr$_{0.45}$NiO$_4$ Sean Giblin, Paul Freeman, Dharmalingham Prabhakaran, Andrew Boothroyd The magnetism of charge stripe ordered La$_{1.55}$Sr$_{0.45}$NiO$_4$ was studied by the combined techniques of neutron diffraction, muon spin relaxation and mass susceptibility. Magnetic ordering was observed at a lower temperature by muon relaxation than neutron diffraction, indicating a glassy transition to the ordered phase, in agreement with the susceptibility. Neutron diffraction determined a second magnetic transition that is observed by all techniques, to be a spin reorientation. On cooling below $T{\rm_{SR}} = 42$\, K the spins re-orientate from lying 33.7$\pm 0.6 ^{\circ}$ away from the stripe direction at 70\,K to 57.4 $\pm 0.4^ {\circ}$ at 10\, K. The magnetic order was observed by neutron diffraction to be of both anisotropic 3D and 2D (without any correlation on the $c$ axis) character. Muon relaxation confirmed this to be consistent with a single magnetically ordered spin stripe phase. The muon site associated with the spin stripe indicated critical behavior expected from a two dimensional magnetically ordered state, whereas the site associated with the charge stripe showed three dimensional critical behavior indicating spin frustration at the charge stripe. [Preview Abstract] |
Tuesday, March 11, 2008 12:27PM - 12:39PM |
J23.00005: Anomalous diffusion on a hypersphere and time structure of two-point spin correlations in short-range-ordered doped oxides. Igor Zaliznyak, Georg Ehlers, Genda Gu Recently, much attention was paid to exploring charge and spin- ordered phases in strongly correlated transition metal oxides, such as superconducting cuprates and related nickelates, manganites and cobaltites. Using elastic neutron scattering, we have investigated the nano-scale structure of short-range charge and spin ordering in a half-doped cobablite La1.5Sr0.5CoO4, and found that they can be understood in the framework of an effective anisotropic 3D random field Ising model. Here we report on the measurement of the time-dependence of the spin- spin correlation function in this material by means of Neutron Spin Echo (NSE) spectroscopy. Our high-precision NSE data exclude simple Arrhenius and stretched-exponential relaxations and can be best described by the model of anomalous diffusion on the appropriate hypersphere. We argue that such time dependence is generic for short-range-ordered spin systems. [Preview Abstract] |
Tuesday, March 11, 2008 12:39PM - 12:51PM |
J23.00006: Transverse displacement modulation of the 1D metallic chains in optimally doped yttrium barium copper oxide superconductor Xuerong Liu, Zahirul Islam, Sunil Sinha, Simon Moss, Jonathan Lang, Ulrich Welp We report on comprehensive quantitative analyses of x-ray diffuse scattering studies of nanoscale inhomogeneities in the optimally doped YBCO superconductor. In addition to previously studied ${\bf q}_0=\left(\frac{1}{4},0,0\right)$ superstructure due to oxygen vacancy ordered ORTHO-IV phase and Huang diffuse scattering due to coherent long-range strain, we present a clear x-ray scattering observation of a transverse displacement modulation of the 1D CuO metallic chains. This modulation co-exists within the well-formed ORTHO-IV patches and persists at temperatures well below $T_c$. Interestingly, the periodicity of this modulation is close to that of $\frac{1}{2k_F}$ according to electronic band calculations. The significance of these modulation and their role in the formation of the electronic inhomogeneities on a nano-meter length scales will be discussed. [Preview Abstract] |
Tuesday, March 11, 2008 12:51PM - 1:03PM |
J23.00007: Investigation of a Model for the Magnetic Properties of RuSr$_2$GdCu$_2$O$_8$ based on the Temperature Dependence of M\"{o}ssbauer Spectra D. Coffey, M. DeMarco, B. Dabrowski, S. Kolesnik, M. Maxwell, S. Toorongian, M. Haka M\"{o}ssbauer spectra were measured from 4.2K to 145K on a $^{99}$Ru enriched sample of RuSr$_2$GdCu$_2$O$_8$ which magnetically orders at 138K and has a full transition to superconductivity at 8.7K with an onset at $\sim$13K. The superconducting transition has no effect on the spectrum which is determined by the hyperfine magnetic field. At low temperatures there is a rapid decrease of this hyperfine magnetic field with increasing temperature indicating a gapless magnon spectrum. We use a local moment model which includes coupling between nearest neighbor in-plane Ru moments and between the Ru moments and Gd moments to calculate the magnon spectrum and use this to estimate the strength of the exchange interactions based on the hyperfine field temperature dependence. The coupling strength is $\sim$250K for Ru-Ru coupling and $\sim$ 15K for Ru-Gd coupling. We discuss the possible microscopic origin of these coupling strengths. [Preview Abstract] |
Tuesday, March 11, 2008 1:03PM - 1:15PM |
J23.00008: Layer Dependence of Charge Distribution and Electronic Structure of HgBa$_2$Ca$_4$Cu$_5$O$_{12}$ Wei-Guo Yin, Dmitri Volja, Wei Ku, Warren Pickett, Deepa Kasinathan Recent experimental observation of layer-dependent properties of the five-layer superconducting cuprate HgBa$_2$Ca$_4$Cu$_5$O$_{12+\delta}$ has inspired intensive interest. In general, multi-layer cuprates are of great interest because the influence of the apical oxygen $p$ states, the main source of the material dependence of cuprate structural and electronic properties [1], could be significantly layer-dependent. In this talk, the layer dependence of the charge distribution and electronic structure of HgBa$_2$Ca$_4$Cu$_5$O$_{12}$ will be investigated via the recently developed many-body Wannier-state method [1]. Possible implications on modulation of local pairing gaps, hole mobility, ``super-repulsion'' [1], and electron-phonon interaction among these distinct CuO$_2$ layers will be discussed, in connection with the intriguing experimental findings of coexisting superconducting and antiferromagnetic orders as well as strong interlayer charge inhomogeneity. Work partially supported by DOE-CMSN. \hspace {0.2cm} [1] W.-G. Yin and W. Ku, cond-mat/0702469. [Preview Abstract] |
Tuesday, March 11, 2008 1:15PM - 1:27PM |
J23.00009: Electron doping of cuprates via interfaces with manganites Elbio Dagotto, Satoshi Okamoto, Seiji Yunoki, Adriana Moreo, Srivenkateswara Kancharla , Atsushi Fujimori The possible electron doping of some undoped high-$T_c$ cuprates via the transfer of charge from undoped manganites (or other oxides) using heterostructure geometries is discussed theoretically [1]. An analysis of photoemission and diffusion voltage experiments locate the Fermi level of some manganites above the bottom of the upper Hubard band of some cuprate parent compounds. The addition of electrons to antiferromagnetic Cu oxides may lead to a superconducting state at the interface with minimal quenched disorder. Model calculations support this view. [1] S. Yunoki et al., Phys. Rev. B {\bf 76}, 064532 (2007) and references therein. [Preview Abstract] |
Tuesday, March 11, 2008 1:27PM - 1:39PM |
J23.00010: Tuning Hole Mobility, Distribution and Repulsion in High-$T_c$ Cuprates via Apical Atoms Wei Ku, Wei-Guo Yin Using a newly developed first-principles Wannier-states approach that takes into account large on-site Coulomb repulsion, we derive the low-energy effective one-band interacting Hamiltonians for several prototypical cuprate superconductors. The material dependence is found to originate primarily from the different energy of the apical atom $p_z$ state. Specifically, the general properties of the low-energy hole state, namely the Zhang-Rice singlet, are significantly modified, via additional intra-sublattice hoppings, nearest-neighbor ``super-repulsion,'' and other microscopic many-body processes. Possible implications on modulation of local pairing gaps, charge distribution, hole mobility, electron-phonon interaction, and multilayer effects will be discussed. [Preview Abstract] |
Tuesday, March 11, 2008 1:39PM - 1:51PM |
J23.00011: Mid-IR band in cuprates : A consequence of strong electron correlations Shiladitya Chakraborty, Dimitrios Galanakis, Philip Phillips Optical conductivity data in lightly doped cuprates show an anomalous peak - like feature in the mid-IR regime ,not naturally expected of doped Mott insulators. Investigating this phenomenon in the light of strong electron correlations, we employ Cluster Dynamical Mean Field Theory (CDMFT) on a four site square plaquette to compute the optical conductivity in the 2-d Hubbard model as a function of hole doping and temperature. The computed optical conductivity shows a peak in the mid-IR regime, consistent with experimental data. Using Non - Crossing Approximation (NCA) as our impurity solver for CDMFT, we have identified the plaquette eigenstates that give rise to the mid-IR feature. The relevant eigenstate has 4 electrons on a plaquette with zero total spin and spatial properties consistent with $d_{x^2 - y^2}$ symmetry. [Preview Abstract] |
Tuesday, March 11, 2008 1:51PM - 2:03PM |
J23.00012: Fluctuation corrections to the conductivity and the Hall conductivity near a spin--density--wave quantum critical point Jie Lin, Andrew Millis On the mean field level, the presence of the spin density wave order gives rise to distinct features in the transport properties of the electron--doped cuprates, which agree qualitatively with experimental data. Here, we determine how fluctuations modify the mean field behavior of the conductivity and the Hall conductivity, with particular attention to the vicinity of the quantum critical point. We developed a theory that respects the spin rotation symmetry. We determine the electron--spin fluctuation vertex and thus the transport and spectral properties of the electrons. Our formulation leads to a correctly gauge-invariant description of the transport properties of the pseudogap state occurring for a 2D Heisenberg system at $T>0$. [Preview Abstract] |
Tuesday, March 11, 2008 2:03PM - 2:15PM |
J23.00013: Inhomogeneous phases of itinerant antiferromagnets Leonid Isaev, Gerardo Ortiz, Cristian D. Batista Although magnetic properties of high-Tc cuprates and heavy fermion compounds has received great attention, only little investigation was performed in the purely antiferromagnetic (AF) phases of these materials. For instance, the mechanism of suppression of the magnetic order was never addressed. In the present work we use a 3D repulsive Hubbard model in an external magnetic field with anisotropic hopping parameters to show that this suppression occurs through a sequence of inhomogeneous states, which are coexisting charge/spin density waves and can be mapped onto the usual Larkin-Ovchinnikov states of type-II superconductors. At the mean-field level we compute the phase diagram of this model as a function of doping and lattice anisotropy. It is shown that morphology of the inhomogeneous phases is determined by the topology of the Fermi surface, which is controlled by the anisotropy (Lifshitz transitions). Insight into the properties of collective modes, such as damping, is gained by computing the magnetic response function in the random phase approximation. Our results are directly applicable to the striped phase of the nickelates and may be useful for understanding the interplay between AF and superconducting orders in the underdoped phase of high-Tc and heavy fermion materials. [Preview Abstract] |
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