Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session V11: Quasiparticle Dispersion and Coupling in Cuprates |
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Sponsoring Units: DCMP Chair: Dan Dessau, University of Colorado at Boulder Room: Morial Convention Center RO9 |
Thursday, March 13, 2008 11:15AM - 11:27AM |
V11.00001: Evidence of Electron Coupling to High Energy Excitations in a High Temperature Superconductor Xingjiang Zhou, Wentao Zhang, Guodong Liu, Lin Zhao, Haiyun Liu, Jianqiao Meng, Xiaoli Dong, Wei Lu, Zhongxian Zhao, Guiling Wang, Hongbo Zhang, Yong Zhou, Zuyan Xu, Yong Zhu, Xiaoyang Wang, Chuangtian Chen, J.S. Wen, Z.J. Xu, Genda Gu, T. Sasagawa We have carried out super-high resolution angle-resolved photoemission measurements on temperature evolution of the electron dynamics along the (0,0)-($\pi$,$\pi$) nodal direction in an optimally-doped Bi$_2$Sr$_2$CaCu$_2$O$_8$ high temperature superconductor. The nodal photoemission spectra exhibit dramatic sharpening with decreasing temperature, with an obvious change in the scattering rate across T$_c$. New high energy features are found to develop at $\sim$115meV and $\sim$150meV, besides the prominent $\sim$70 meV one, in the nodal electron self-energy in the superconducting state. These observations provide evidence that, in addition to coupling with low energy excitations like phonons or magnetic resonance mode, there are high-energy excitations involved in the electron coupling. [Preview Abstract] |
Thursday, March 13, 2008 11:27AM - 11:39AM |
V11.00002: High energy kink in the single particle spectra of the two-dimensional Hubbard model Alexandru Macridin, Mark Jarrell, Thomas Maier, Douglas Scalapino Employing dynamical cluster quantum Monte Carlo calculations we show that the single particle spectral weight $A(k,\omega)$ of the one-band two-dimensional Hubbard model displays a high energy kink in the quasiparticle dispersion followed by a steep dispersion of a broad peak similar to recent ARPES results reported for the cuprates. Based on the agreement between the Monte Carlo results and a simple calculation which couples the quasiparticle to spin fluctuations, we conclude that the kink and the broad spectral feature in the Hubbard model spectra is due to scattering with damped high energy spin fluctuations. [Preview Abstract] |
Thursday, March 13, 2008 11:39AM - 11:51AM |
V11.00003: Theory of quasiparticle excitations in cuprates: universal Fermi velocity and high energy anomalies Qiang-Hua Wang Recent measurements of quasiparticles in hole-doped cuprates reveal highly unusual features: 1) the doping-independent Fermi velocity, 2) two energy scales in the quasiparticle spectral function, and 3) a suppression of the low energy spectral weight near the zone center. The underlying mechanism is under hot debate. We addressed these important issues by a new mean field theory and a novel variational Monte Carlo (VMC) study of the t- J model. We obtained results in both approaches in agreement with the experiments but without invoking extrinsic effects. They reflect the role of strong correlations in the form of local Mottness and antiferromagnetic fluctuations, yielding a strong connection between the low and high energy quasiparticle excitations. Besides, we resolved a long standing issue of the sum rule for quasiparticle spectral weights in traditional VMC studies. The electron doped case was also discussed and we concluded that no high energy anomaly exists in the occupied side, in contrast to the hole doped case. [Preview Abstract] |
Thursday, March 13, 2008 11:51AM - 12:03PM |
V11.00004: Dispersion and Spectral weight analysis of ``waterfall'' structure in Pb doped Bi2212. Qiang Wang, Zhe Sun, Eli Rotenberg, Helmut Berger, Daniel Dessau Angle resolved photoemission spectroscopy (ARPES) is used to investigate the property of the ``waterfall'' structure in (Bi, Pb)2Sr2CaCu2O8. The dispersion analysis of the spectrum shows that there is not a ``universal high energy scale'' in this material. And the spectral weight analysis suggests that the matrix element and the inelastic scattering may have an important role in the formation of the waterfall structure. [Preview Abstract] |
Thursday, March 13, 2008 12:03PM - 12:15PM |
V11.00005: Magnon Corrections to Cuprate Self Energy Robert Markiewicz, Tanmoy Das, Arun Bansil Recently, high energy kinks (`waterfalls') have been reported above 200 meV in the ARPES spectra of several cuprates. These kinks are a signal of bosonic coupling and may be responsible for the band renormalizations found at lower energies. We have shown that coupling to collective modes in the spin channel can yield waterfall-like effects in the electronic dispersion in the electron as well as hole doped cuprates. [1] Here we further explore the effects of the magnons in the pseudogap regime, including a discussion of how magnons influence optical properties. \newline \newline [1] R.S. Markiewicz, S. Sahrakorpi, and A. Bansil, cond- mat/0701524, to be published, PRB. [Preview Abstract] |
Thursday, March 13, 2008 12:15PM - 12:27PM |
V11.00006: Aspects of the electron-phonon interaction in the Cuprates Steve Johnston, Wei-Sheng Lee, Thomas Devereaux, Z.X. Shen The ubiquity of the ``kink''-structures observed in the band-dispersion of the High-Tc cuprates have made this feature the subject of debate for many years now. At present, the community agrees that the feature is due to electron-boson coupling to a collective mode, however, a consensus has yet to be reached on its identity. In this talk we will review the arguments typically made against the phonon interpretation, which are grounded in knowledge gained from metallic systems. We will then show the complications one encounters in extrapolating from these systems to strongly correlated systems such as the cuprates. We will also discuss some of the common methods for extracting information from photoemission spectra that are cited in the modern literature in order to highlight the strengths and weaknesses of each and their reliability for extracting realistic estimates for parameters such as the electron-boson coupling strength $\lambda$. [Preview Abstract] |
Thursday, March 13, 2008 12:27PM - 12:39PM |
V11.00007: Phonon anomaly in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$* Jiandong Guo, Huajun Qin, Kehui Wu, R. G. Moore, E. W. Plummer, J. Wen, G. D. Gu, Jiandi Zhang Electron-phonon coupling (EPC) plays in many exotic phenomena displayed by strongly-correlated electron materials, such as the pairing mechanism in high-$T_{C}$ superconductors and metal-insulator transition in ruthenates. Many studies show a strong renormalization of quasi-particle band structure near Fermi energy associated with the coupling to boson modes $\sim $40-50 meV. However, there is no clear picture of the origin of these modes. With angle-resolved electron energy loss spectroscopy, we have studied the lattice dynamics of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ surface. The data indicate a phonon anomaly of modes $\sim $50 meV, identified as the in-plane Cu-O stretching modes, where the energy shifts (softens) while the spectral linewidth and weight vary along (0,0)-($\pi $,0) direction. The other feature $\sim $80 meV, attributed to apical oxygen vibrations, exhibits distinct dispersion toward ($\pi $,$\pi )$. Such behaviors are observed both above and below the superconducting T$_{C}$. These detailed measurements provide new insights into the nature of EPC in such materials. * Supported by China NSF-10704084, NSF DMR-0346826, NSF and DOE (NSF-DMR-0451163 and DMS{\&}E). [Preview Abstract] |
Thursday, March 13, 2008 12:39PM - 12:51PM |
V11.00008: Isotope effect on the nodal kink energy in Bi2212 J.F. Douglas, H. Iwasawa, K. Satou, H. Eisaki, Y. Yoshida, H. Bando, T. Saitoh, A. Ino, M. Taniguchi, M. Arita, K. Shimada, H. Namatame, T. Masui, S. Tajima, S. Uchida, Y. Aiura, D.S. Dessau Using low energy angle resolved photoemission spectroscopy (le-ARPES), we have observed an energy shift of the nodal kink upon substitution of $^{18}$O for $^{16}$O in optimally doped (T$_{c}\sim $92K) Bi2$_{.1}$Sr$_{1.9}$CaCu$_{2}$O$_{8+\delta }$. Studying several samples of each isotope, we find that the kink energy decreases by 3.22 $\pm $ 0.72 meV upon $^{18}$O substitution, in good agreement with the energy shift one would expect from a phononic mode. This strongly supports the view that the nodal dispersion kink arises from electronic coupling to a phonon mode. [Preview Abstract] |
Thursday, March 13, 2008 12:51PM - 1:03PM |
V11.00009: Theory of Kink Structure of Quasi-Particle Energy Dispersion in Photoemission Spectra of High Temperature Superconducter Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ via Dipolon Mediated Electron-Electron Pairing Mechanism Ram Sharma We have made use of the four-momenta space diagrams in the dressed particle picture to write the self-energy $\Sigma(p)$ by taking the sum of the exchange diagrams involving dipolon propagator, electron Green's function and electron-electron Coulomb interaction to obtain single quasi-particle energy dispersion in high $T_C$ $\backslash$ Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ superconductors. The theory contains Mott renormalization and all important and necessary electron correlations. This constitutes an extension of the strong-coupling dipolon theory [1,2] which explains [3] also the peak-dip-hump structure of the line shape of the photoemission spectra of high $T_C$ superconductors. Our calculations of the single quasi-particle energy dispersion for $\backslash$ Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ show a strong kink at the binding energy near 60 meV which has already been identified in the experiments [4] and predicts two additional weak kinks at binding energies close to 100 and 160 meV, yet to be identified experimentally. The Migdal vertex correction does not change our results drastically. [1] R. R. Sharma, Phys. Rev. {\bf B 63}, 054506 (2001). [2] R. R. Sharma, Physica {\bf C 439}, 47 (2006). [3] R. R. Sharma, Physica {\bf C}, in press. [4] P. V. Bogdanov et al., Phys. Rev. Lett. {\bf 85}, 2581, 2000. [Preview Abstract] |
Thursday, March 13, 2008 1:03PM - 1:15PM |
V11.00010: Fermi Surface Topology Effects on the Electron-Phonon Coupling in Electron-doped Cuprates S.R. Park, D.J. Song, C.S. Leem, Chul Kim, C. Kim, B.J. Kim, H. Eisaki We have performed high resolution angle resolved photoemission (ARPES) studies on electron doped cuprate superconductors Sm$_{2-x}$Ce$_{x}$CuO$_{4}$ ($x$=0.10, 0.15, 0.18). Imaginary parts of the electron removal self energy by a newly developed method shows kink-like features due to electron-bosonic mode coupling. The kink-like feature is seen along both nodal and anti-nodal directions but at different energies of 50 and 70 meV. Such energy scales can be reconciled by taking the Fermi surface topology and phonon dispersions into account, revealing the kink structures are due to the electron-phonon coupling. Estimated electron-phonon coupling constant $\lambda $ from the self energy is about 0.6 independent of doping and is isotropic. In addition to the low energy feature, we observe a hump structure at 350 meV which is anisotropic and exists only in the anti-nodal spectrum. [Preview Abstract] |
Thursday, March 13, 2008 1:15PM - 1:27PM |
V11.00011: Theoretical fits of laser-ARPES energy distribution curves of the high Tc superconductor Bi2212 N.C. Plumb, P.A. Casey, J.D. Koralek, J.F. Douglas, Z. Sun, Y. Aiura, K. Oka, H. Eisaki, P.W. Anderson, D.S. Dessau Laser-ARPES has produced spectral lineshapes in photoemission that are much sharper than any previous data, which is due to increased energy and momentum resolution, increased bulk sensitivity, and decreased final state broadening. The lifetimes of these states, extracted from simple Lorentzian fits to the data, are consistent with bulk-sensitive optical data, implying that we are for the first time measuring the intrinsic spectral function. It therefore is appropriate to study the spectral lineshape in detail. We have looked at standard Lorentzian energy distribution curves, as well as extensions based upon Fermi Liquid theory, Marginal Fermi Liquid theory, and of great interest, a non-Fermi Liquid theory based upon Anderson's treatment of the Gutzwiller projection. The lineshapes based upon the Gutzwiller projection utilize only one free parameter and include no background term, yet they fit the data well over a broad range of temperatures and energies. [Preview Abstract] |
Thursday, March 13, 2008 1:27PM - 1:39PM |
V11.00012: Properties of high-T$_C$ superconductors from spin-phonon coupling and band models. Thomas Jarlborg An understanding of the rich doping- and $(\vec{q},\omega)$-dependences of spin excitations in high T$_C$ materials is essential since the mechanism of high-T$_C$ superconductivity might be linked to spin fluctuations. Ab-initio band calculations show important spin-phonon coupling (SPC), i.e. antiferromagnetic fluctations are enhanced when they co-exist with $\vec{q}_x$-phonons involving O, Cu or La distortions. Parameters for these ``1-dimensional'' (1D) electron-phonon and spin-wave couplings are obtained from band calculations for long supercells containing phonon distortions and/or staggered fields. The characteristic 2-D q-dependence of the excitations are calculated for a free-electron like band with the use of the ab-initio parameters. The q-variation depend on the strength of the SPC, which leads to a linear relation between $\vec{q}$ and doping, x, for x$\leq$0.15. The SPC is strongest for in-plane O-modes, weaker for modes involving the heavy atoms, and smallest for apical O, which together with SPC for the phonons at the characteristic frequency lead to a q-dependent excitation spectrum. These and other properties coming from SPC in the band/free-electron model compare favorably with observations. [Preview Abstract] |
Thursday, March 13, 2008 1:39PM - 1:51PM |
V11.00013: Universal dispersion anomalies revealed by DQMC simulations of the Hubbard model B. Moritz, S. Johnston, W. Meevasana, C. Kim, T. P. Devereaux, R. T. Scalettar, Z.-X. Shen The recent observation of a ``high energy anomaly" (HEA) in hole-doped high-Tc compounds, as well as the half-filled parent insulators, using angle-resolved photoemission spectroscopy (ARPES) has sparked a great deal of interest and intense theoretical and experimental investigations. Using determinant quantum Monte Carlo (DQMC) and maximum entropy analytic continuation (MEM), we investigate the existence of the HEA in the single-band Hubbard model. The spectral functions obtained from the simulations reveal a universal HEA across the doping spectrum, similar to that seen in experiment. This signals a cross-over from a quasiparticle-like band at low energy to the incoherent lower Hubbard band at higher energy. A comparison of the self-energy obtained from simulation to that extracted from experiment serves as a further llustration of the similarities. In addition, we perform simulations of the single-band Hubbard model on the electron-doped side of the phase diagram and compare and contrast our results to existing experimental evidence and comment on the possibility that future experiments would find a universal HEA in electron-doped compounds. [Preview Abstract] |
Thursday, March 13, 2008 1:51PM - 2:03PM |
V11.00014: Local effects of apical oxygen on superconductivity in high-$T_{\rm c}$ cuprates Michiyasu Mori, Takami Tohyama, Sadamichi Maekawa The superconducting critical temperature ($T_{\rm c}$) of high- $T_{\rm c}$ cuprates widely distributes among various series of crystal structures, even if the doping rate is optimized in the CuO$_2$ planes. In addition, the $T_{\rm c}$ is enhanced by applying pressure[1]. These material- and pressure dependences have meaningful correlation with an energy difference of oxygen sites in an apical site and in the CuO$_2$ plane ($V_{\rm A}$)[2]. On the other hand, Slezak et al. has found that locally modulated gap energy has anti-correlation with a distance between a Cu- and an apical O-sites, i.e., the larger distance is related to the smaller gap energy[3]. We study such a local effect of apical oxygen on superconductivity by calculating the Madelung potential. In particular, we focus on a local variation of $V_{\rm A}$, whose value approximately corresponds to stability of the Zhang- Rice singlet state[2]. It is found that, on neighboring sites of apical sites close to Cu sites, $V_{\rm A}$ are locally enhanced compared to other sites. To estimate the gap energy, we propose a toy model like a BCS mean field Hamiltonian with an additional degree of freedom, which describes a role of apical oxygen. We will discuss an anti-correlation between the gap energy and the position of apical oxygen. [1] N. Tanahashi et al: Jpn. J. Appl. Phys. 28, L762 (1989). [2] Y. Ohta, T. Tohyama, and S. Maekawa: Phys. Rev. B 43, 2968 (1991). [3] J. Slezak, PhD thesis. [Preview Abstract] |
Thursday, March 13, 2008 2:03PM - 2:15PM |
V11.00015: Variable Temperature Scanning Tunneling Spectroscopy of Inhomogeneous High Temperature Superconductors E.W. Hudson, M. C. Boyer, W.D. Wise, Kamalesh Chatterjee, Yayu Wang, Takeshi Kondo, Tsunehiro Takeuchi, Hiroshi Ikuta Scanning Tunneling Microscopy (STM) of the high temperature superconductor $Bi_2Sr_2CaCu_2O_{8+x}$ (Bi-2212) long ago revealed large gap variations on nanometer length scales. In this talk I will discuss new results from our temperature dependent STM studies of Bi-2201. In particular, I will focus on the effects of these variations on other observables, such as the states generated around single atom impurities, as well as on other measurement techniques, such as angle resolved photoemission (ARPES). [Preview Abstract] |
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