Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session W32: Focus Session: High Tc Cuprates: Theory and Computation |
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Sponsoring Units: DCOMP DCMP Chair: Alexander Balatsky, LANL Room: LACC 507 |
Thursday, March 24, 2005 2:30PM - 2:42PM |
W32.00001: The role of doping, pressure and composition on the creation of holes in high T$_c$ cuprates Claudia Ambrosch-Draxl, Timo Thonhauser, Eugene Ya. Sherman We present a series of first-principles calculations for Hg based high $T_c$ cuprates investigating the effect of pressure, doping, and composition on the formation of charge carriers. In particular, the total and site-projected hole concentration in the CuO$_2$ planes and the density of states are studied in detail. We also discuss effects of inhomogeneity introduced by doping and the limitations on creating holes by either doping, pressure, or the number of CuO$_2$ layers per unit cell. From an analysis and comparison of our results to available experimental data on the pressure dependence of $T_c$, we conclude that the effective coupling constant to the boson mediating the Cooper pairing is of the order of $1$ ruling out the weak coupling approaches. [Preview Abstract] |
Thursday, March 24, 2005 2:42PM - 2:54PM |
W32.00002: Electron- and Spin-Density Distributions around Zn Impurities in Cuprates Christophe Bersier, Samuel Renold, Erich P. Stoll, Peter F. Meier, Tom A. Claxton First-principles density-functional calculations have been performed with clusters comprising up to thirteen copper atoms in the CuO$_2$-plane for La$_2$CuO$_4$, YBa$_2$Cu$_3$O$_7$ and YBa$_2$Cu$_4$O$_8$. The differences in the electron- and spin-density distributions that occur upon replacing one planar Cu by a Zn atom are worked out. In general, the charge densities at the oxygens adjacent or in the next shell to Zn are smaller than those calculated without Zn. Simulating in addition the influence of hole doping, it is found that Zn repels holes and favors the formation of antiferromagnetic bubbles in its neighborhood. Furthermore, a comparison of the calculated electric field gradients (EFGs) with NMR and NQR data on Zn substituted cuprates suggests that the copper satellite peaks with an EFG value somewhat smaller than that of the main line are due to Cu which are second nearest neighbors to Zn. For Cu atoms adjacent to Zn, the calculated EFG values are marginally larger and will contribute to broaden the main line. [Preview Abstract] |
Thursday, March 24, 2005 2:54PM - 3:06PM |
W32.00003: Ab-initio electronic structure computation of atomic displacements in an underdoped YBCO superconductor Didier deFontaine, Vidvuds Ozolins Recent diffraction studies have shown the existence of lattice modulations in yttrium barium cuprates (YBCO). We show that these modulations are caused by the ordering of O-Cu-O- chains in the CuO planes. Remarkable agreement is illustrated in the case of underdoped YBCO between experimental diffraction patterns of diffuse intensity and satellite intensity obtained from \textit{ab initio} electronic structure calculations. It is suggested that the "stripe" structure of magnetic excitations observed by inelastic neutron scattering originates in the underlying oxygen order described herein. [Preview Abstract] |
Thursday, March 24, 2005 3:06PM - 3:18PM |
W32.00004: Ab Initio Calculation of Impurity Effects in Copper Oxide Materials Lin-Lin Wang, Hai-Ping Cheng, P.J. Hirschfeld We describe a method for calculating, within density functional theory, the electronic structure associated with typical defects which substitute for Cu in the CuO2 planes of high-Tc superconducting materials. The focus is primarily on BSCCO-2212, the material on which most STM measurements of impurity resonances in the superconducting state have been performed. The magnitudes of the effective potentials found for Zn, Ni and vacancies on the in-plane Cu sites in this host material are remarkably consistent with phenomenological fits of potential scattering models to STM resonance energies. The effective potential ranges are quite short, of order 1 Å with weak long range tails. For the case of Zn and Cu vacancies, the effective potentials are strongly repulsive, and states on the impurity site near the Fermi level are simply removed. The local density of states (LDOS) just above the impurity is nevertheless found to be a maximum in the case of Zn and a local minimum in case of the vacancy, in agreement with experiment. The Zn and Cu vacancy patterns are explained as due to the long-range tails of the effective impurity potential at the sample surface. The case of Ni is richer due to the Ni atom’s strong hybridization with states near the Fermi level; in particular, the short range part of the potential is attractive, and the LDOS is found to vary rapidly with distance from the surface and from the impurity site. We propose that the current controversy surrounding the observed STM patterns can be resolved by properly accounting for the effective impurity potentials and wave-functions near the cuprate surface. [Preview Abstract] |
Thursday, March 24, 2005 3:18PM - 3:30PM |
W32.00005: Fourier-Transformed Inelastic STM Tunneling into High-Temperature Jian-Xin Zhu, A.V. Balatsky There are heightened interest in relating the STM observations with other spectroscopy measurements with momentum resolution in high-$T_{c}$ cuprates. We have proposed earlier that STM can be used to detect the $41\;\mbox{meV}$ $(\pi,\pi)$ mode as observed in neutron scattering experiments. Recent ARPES on optimally doped Bi$_2$Sr$_2$Ca$_{0.92}$Y$_{0.08}$Cu${_2}$O$_{8+\delta}$ suggests an anisotropic electron-phonon coupling. Here we address the role of these phonons (O B1g mode and in-plane Cu-O breathing mode) and the Fourier-transformed STM features they might generate in the local density of states. We also look into the effect of a distributed random potential on these features. The Fourier-transformed inelastic electron tunneling spectrocopy STM would allow one to extract the Eliashberg function in both frequency and momentum space, if successful. [Preview Abstract] |
Thursday, March 24, 2005 3:30PM - 3:42PM |
W32.00006: Strongly momentum dependent electron-phonon coupling in high temperature superconductors Tanja Cuk, Felix Baumberger, Donghui Lu, Nik Ingle, Xing-Jiang Zhou, Hiroshi Eisaki, Nobuhisa Kaneko, Zahid Hussain, Thomas Devereaux, Naoto Nagaosa, Zhi-xun Shen Early results on the electron-phonon coupling constant extracted from momentum averaged experiments on the cuprates suggest small values ($\sim $ 0.1). Recent angle resolved photoemission (ARPES) experiments reveal that electron-phonon coupling in the cuprates has pronounced momentum dependence. We explore manifestations of electron-phonon coupling in the ARPES data for two phonon modes that show renormalizations in Raman spectroscopy and neutron scattering. We find that the out-of-plane, out-of-phase O buckling mode $\sim $ 35meV (B$_{1g})$ involves small momentum transfers and couples strongly to electronic states near the anti-node while the in-plane $\sim $ 70meV Cu-O breathing modes involve large momentum transfers and couple strongly to nodal electronic states. A calculation based on Eliashberg theory, simple symmetry considerations, and kinematic constraints has for the first time described the mode-coupling behavior throughout the brillouin zone in both normal and superconducting states for optimally doped Bi$_{2}$Sr$_{2}$Ca$_{0.92}$Y$_{0.08}$Cu$_{2}$O$_{8+delta}$. The data are consistent with a lambda $\sim $ 3 at the maximum of the d-wave gap, but a momentum averaged lambda $\sim $ 0.2. These results suggest that a momentum-sensitive probe is a necessary component for determining coupling constants in the cuprates. [Preview Abstract] |
Thursday, March 24, 2005 3:42PM - 3:54PM |
W32.00007: Evolution of Mid-gap States and Residual 3-Dimensionality in La$_{2-x}$Sr$_x$CuO$_4$ Arun Bansil, Seppo Sahrakorpi, Matti Lindroos, Robert Markiewicz We have carried out extensive first principles doping-dependent computations of angle-resolved photoemission (ARPES) intensities in La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) over a wide range of binding energies. Intercell hopping and the associated 3-dimensionality, which is usually neglected in discussing cuprate physics, is shown to play a key role in shaping the ARPES spectra. Despite the obvious importance of strong coupling effects (e.g. the presence of a lower Hubbard band coexisting with mid-gap states in the doped insulator), we show that a number of salient features of the experimental ARPES spectra are captured to a surprisingly large extent when effects of $k_z$-dispersion are properly included in the analysis. Work supported in part by the U.S.D.O.E. [Preview Abstract] |
Thursday, March 24, 2005 3:54PM - 4:06PM |
W32.00008: Particle-Hole Asymmetry in Doped Mott Insulators: Implications for Tunneling and Photoemission Spectroscopies Mohit Randeria, Rajdeep Sensarma, Nandini Trivedi, Fu-Chun Zhang In a system with strong local repulsive interactions it should be more difficult to add an electron than to extract one. We make this idea precise by deriving various exact sum rules for the one-particle spectral function independent of the details of the Hamiltonian describing the system and of the nature of the ground state. We extend these results using a variational ansatz for the superconducting ground state and low lying excitations. Our results shed light on the striking asymmetry in the tunneling spectra of high Tc superconductors and should also be useful in estimating the local doping variations in inhomogeneous materials. [Preview Abstract] |
Thursday, March 24, 2005 4:06PM - 4:18PM |
W32.00009: Mott gap collapse in electron- and hole-doped cuprates within a four-band Hubbard Model Hsin Lin, R.S. Markiewicz, A. Bansil We discuss the issue of Mott gap collapse within a selfconsistent mean field framework using a four-band Hubbard model which includes Cu $4s$ orbitals. The evolution with doping of the Fermi surface of Nd$_{2-x}$Ce$_x$CuO$_4$ (NCCO) has been investigated previously by Kusko, et al.[1] in a one-band t-t$'$-t$''$-U Hubbard model using related ARPES results[2]. The four-band model in this work confirmed the findings of the one-band model that it is necessary to employ a doping-dependent U, where U decreases with increasing doping. We also consider the hole-doped case in order to understand the doping- dependence of the peak-dip-hump structure in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. Work supported in part by the USDOE.\\ $\mbox{[1]}$C. Kusko, R.S. Markiewicz, M. Lindroos, and A. Bansil, Phy. Rev. B {\bf 66}, 140513 (2002).\\ $\mbox{[1]}$N.P. Armitage et al, Phy. Rev. Lett. {\bf 88}, 257001 (2002). [Preview Abstract] |
Thursday, March 24, 2005 4:18PM - 4:30PM |
W32.00010: Analysis of the renormalization of the quasiparticle dispersion in high-$T_{c}$ superconductors Jian-Xin Li$^{1,3}$, Tao Zhou$^1$, Z.D. Wang$^2$ Based on the slave-boson approach to the bilayer $t-t^{\prime}- J$ model, the renormalization of the quasiparticle dispersion in high-$T_{c}$ cuprates is investigated by examining both interactions of fermions with spin fluctuations and phonons. It is shown that both interactions can give rise to a kink in the dispersion around the antinodes of the $d$-wave gap (near $(\pi,0)$ and $(0,\pi)$). However, three remarkable differences caused by these interactions are found, namely the peak/dip/hump structure in the quasiparticle lineshape, the doping dependence of the quasiparticle weight, and the role played by the interlayer coupling on the formation of the antinodal kink. These differences are suggested to serve as a discriminance to single out the main residual interaction in the superconducting state. A comparison to the recent angle-resolved photoemission (ARPES) experiments shows that the coupling to the spin resonance dominates for quasiparticles around the antinodes. \newline \newline $^{1}$National Laboratory of Solid State of Microstructure and Department of Physics, Nanjing University, Nanjing 210093, China\\ $^{2}$Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China\\ $^{3}$The Interdisciplinary Center of Theoretical Studies, Chinese Academy of Science, Beijing 100080, China. [Preview Abstract] |
Thursday, March 24, 2005 4:30PM - 4:42PM |
W32.00011: Downward Shift of Infrared Spectral Weight in the Pseudogap State of Cuprates: Role of Anisotropy Rouzbeh Gerami, Chetan Nayak Transfer of the infrared spectral weight (SW) in the cuprate superconductors as they enter the pseudogap phase has been studied. Using the linear response theory and based on the theory of $d$- density wave order for the pseudogap phase, the optical conductivity is calculated. It is shown that the unexpected downward transfer of the spectral weight, as observed in recent optical experiments, can be explained by considering the anisotropy of the quasiparticle scattering rate. Two different behaviors in the direction of the spectral weight shift are observed: For the (unrealistic) isotropic choice of the scattering rate, SW shifts upward, while the (realistic) anisotropic choice generates a downward SW shift, as observed in the experiment. [Preview Abstract] |
Thursday, March 24, 2005 4:42PM - 4:54PM |
W32.00012: Modulation of Local Density of States within the d-density Wave Theory in the Underdoped Cuprates Sudip Chakravarty, Amit Ghosal, Angela Kopp Intriguing results have been found in the recent high resolution scanning tunneling studies, pointing to the emergence of a new order in underdoped high $T_c$ cuprates. Motivated by these results we calculated the Fourier transform spectrum of the local density of states of underdoped cuprates within the framework of a fully self-consistent Bogoliubov-de Gennes mean field theory. Our calculation is carried out for coexisting d-density wave and d-wave superconducting states in the presence of a low concentration of unitary impurities taking into account the fluctuations in the order parameters as well as the correlation between impurities. Based on our results, we propose that a d-density wave ordered state captures much of the essential physics of these spatial modulations. Our results on the nature of the modulations, their robustness and very weak dispersions of certain Fourier peaks are consistent with primary experimental findings in the underdoped BSCCO at very low temperatures.\\ This work was supported by the NSF (DMR-0411931). [Preview Abstract] |
Thursday, March 24, 2005 4:54PM - 5:06PM |
W32.00013: Magnetic field dependent of the local density of states in cuprate superconductors Hong-Yi Chen, Q. Wang, C.S. Ting The d-wave superconductivity ($d$SC) with competing antiferromagnetic (AF) order as a function of magnetic fields $B$ has been studied by using a phenomenological $t-t'-U-V$ model and the Bogoliubov-de Gennes$'$ equations. Our calculations are performed in a magnetic field $B$ ranging from about $9T$ to $54T$ which corresponding to the magnetic unit cell with size from $40\times 80$ to $16\times 32$. Without the AF order $(U=0)$, the system is in the pure $d$SC state. We show that the local density of states (LDOS) far from the vortex core at the Fermi energy is proportional to $\sqrt{B}$ for $B<18T$, in agreement with the Volovik’s result. For $U=2.42$, we show that the field induced spin-density-wave (SDW) appears and it has the stripe-like structure with a periodicity of $8a$. The amplitude of the induced SDW stripes decreases as the strength of $B$ is reduced. We also point out that the LDOS at the Fermi energy far from the vortex core does not follow the Volovik’s prediction when the induced SDW is in presence. [Preview Abstract] |
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