4PO4-10
D.L. Feng 1, W.J. Zheng 1, K.M. Shen 1, D.H. Lu 1, F. Ronning 1, and Z.-X. Shen 1, J.-i. Shimoyama 2, K. Kishio 2, G. Gu 3, and D. Van der Marel 4. 1 Department of Physics, Applied Physics and Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305, USA. 2 Department of Applied Chemistry, University of Tokyo, Tokyo, 113-8656, Japan. 3 School of Physics, University of New South Wales, P.O. Box 1, Kensington, NSW, Australia 203. 4 Material Science Center, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Presenting Author: D.L. Feng
The Fermi surface of the Bi2212 system is systematically studied using a variety of photon energies. In addition to reconciling the conflicting reports on the Fermi surface of this important material, we identify almost perfectly nested Fermi surface segments parallel to the (1,0) or (0,1) direction. This general yet long overlooked feature of the Fermi surface is intriguingly similar to the Fermi surface of the La1.48Nd0.4Sr0.12CuO4 system. The nested Fermi surface segment would favor a charge density wave instability which is commensurate with the lattice at 1/8 doping.
4PO4-11 The ARPES Pseudogap and Anomalous Background as Evidence for a Fermi Level Band Crossing
Jason Perry and Jamil Tahir-Kheli, First Principles Research, Inc., 8391 Beverly Blvd., #171, Los Angeles, CA 90068
Presenting Author: J.K. Perry
We show that the unusual observation of a pseudogap in the normal state of underdoped BiSCO 2212 using angle resolved photoemission spectroscopy (ARPES) is consistent with a new band structure for the cuprate superconductors in which the x2-y2 and z2 bands are seen to cross at the Fermi level (Phys. Rev. B 58, 12307 (1998); Ibid, 12323; J. Phys. Chem., in press; Phys. Rev. Lett., submitted). Limitations in the experimental method prevent the narrow 3D z2 band from being fully resolved, leading instead to a broad background with "stepfunction" character. As a consequence, the Fermi surface is mis-assigned and a pseudogap of approximately d-wave symmetry develops.
4PO4-12 Flat Bands and Superconductivity
R. Gatt 1, A. Kaminski 1, J. Mesot 1, H. Fretwell 1, H. Ding 2, T. Sato 3, T. Yokoya 3, T. Takahashi 3, T. Takeuchi 4, T. Mochiku 5, and J.C. Campuzano 1. 1 Physics Dept., University of Illinois at Chicago, Chicago IL 60607. 2 Department of Physics, Boston College, Chestnut Hill, MA 02467. 3 Department of Physics, Tohoku University, 980-8578 Sendai, Japan. 4 Department of Crystalline Materials Science, Nagoya University, Nagoya 464-01, Japan. 5 National Research Institute for Metals, Sengen, Tsukuba, Ibaraki 305, Japan.
Presenting Author: R. Gatt
We wish to examine the relation between normal state electronic structure and superconductivity, particularly the development of the flat band region close to (0,p ) as function of doping. Pb-Bi2201 is a single layer cuprate with a high quality cleavage plane. Pb doping relaxes the mismatch between Cu-O and Bi-O planes. Oxygen doping allows the continuous variation of Tc from 14K in the underdoped side to 0K in the overdoped side. It's relatively low Tc allows for high resolution angular resolved photoemission measurements in the normal state. It is thus a perfect material to study the electronic structure of the cuprates as function of doping, avoiding the complications of multiple Cu-O layers and superlattice effects. Here we examine the dispersion and lifetime broadening of the states near (0,pi) as function of doping, with a view to try to understand the origin of the flat bands, and any possible correlation to Tc.
4PO4-13 OD Bi2212: Signature of the Pairing Boson in the k-Dependence of the Superconducting Gap
R. Gatt 1, Y. Hirai 1, S. Christensen 1, B. Frazer 1, R.J. Kelley 1, M. Onellion 1, I. Vobornik 2, L. Perfetti 2, G. Margaritondo 2, C. Kendziora 3, A. Morawski 4, T. Lada 4, and A. Paszewin 4. 1 Physics Department, University of Wisconsin-Madison, 1150 Univ. Ave., Madison, WI 53706. 2 Inst. Physique Appliquee, EPFL, CH-1015 Lausanne, Switzerland. 3 NRL, Washington, D.C. 20011. 4 Unipress, Polish Academy of Sciences, Warsaw, Poland.
Presenting Author: R. Gatt
Angular resolved photoemission was used to measure the k-dependence of the superconducting gap in overdoped Bi2212. While the node at 45 degrees is conserved, there are substantial deviations from a first order d-wave away from the node. The pairing susceptibility is peaked at special regions on the Fermi surface. Comparison of these results with a detailed mapping of the Fermi surface reveals the extension and location of these hot regions. We attribute this behavior to a signature of the pairing boson. Using these hot regions as a smoke detector, we identify spin fluctuations as the most probable source of fire.
4PO4-14 The Fermi surface of Bi2212-based HTSC from angle-scanned photoemission with high energy and angular resolution.
M.S. Golden 1, S.V. Borisenko 1, S. Legner 1, C. Duerr 1, M. Knupfer 1, J. Fink 1, G. Yang 2, S. abell 2, and H. Berger 3. 1 IFW Dresden, Institute for Solid State Research, P.O. Box 270016, D-01171 Dresden, Germany. 2 School of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, United Kingdom. 3 Institut de Physique Appliquee, Ecole Polytechnique Federale, CH-1015 Lausanne, Switzerland.
Presenting Author: M.S. Golden
We present ARPES data from Bi2212 and Pb-doped Bi2212 recorded in the angle-scanned mode. The data were taken using monochromated He I radiation from high quality single crystals with angular and energy resolutions of 0.7° and 25 meV. By taking an extremely dense k-space mesh (typically ca. 1500 k-points per quadrant), we can build up a complete picture of the occupied electronic states to a depth of ca. 600meV below the Fermi level, covering one or more quadrants of the Brillouin zone from a single cleave. Thus our Fermi surface maps are based wholly upon 'real', uninterpolated experimental data.
In this contribution we concentrate on the topology of the main and shadow Fermi surfaces in these systems, indicating a possible reconciliation of the current ARPES controversy regarding the shape of the FS in the 2212 materials. Furthermore, an analysis of the EDC's underlying the constant energy surfaces recorded below Tc reveals the detailed behaviour of the pile-up peak, dip etc. also away from the high symmetry directions.
Thanks for financial support to: BMBF (05SB8 BDA6), DFG (Graduiertenkolleg 'Struktur- und Korrelationseffekte in Festkoerpern').
4PO4-15 Topology of the Fermi surface of Bi-2212 from high resolution ARPES
S. Borisenko 1, S. Legner 1, C. Duerr 1, M. Knupfer 1, M.S. Golden 1, J. Fink 1, G. Yang 2, S. Abell 2, and H. Berger 3. 1 IFW Dresden, Institute for Solid State Research, P.O. Box 270016, D-01171 Dresden, Germany. 2 School of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, United Kingdom. 3 Institut de Physique Appliquee, Ecole Polytechnique Federale, CH-1015 Lausanne, Switzerland.
Presenting Author: S.V. Borisenko
We have investigated Bi-2212 and Pb-doped Bi-2212 single crystals using angle-scanned photoemission. Our experimental set-up allows the acquisition of EDC's with angular and energy resolutions of 0.2-0.7° and 25 meV across a wide angular region (0 < polar < 50°, 0 < azimuth < 200°). In this way, we can obtain a complete ARPES dataset from the occupied electronic states to a depth of ca. 600 meV below the Fermi level, covering one or more quadrants of the Brillouin zone from a single cleave with an extremely high density of spectra in k-space. The spectra are recorded with monochromatised, but unpolarised He I radiation, thus avoiding the complications inherent in such angle-scanned ARPES investigations using polarised synchrotron radiation.
We address the current debate regarding the 'true' FS topology of the 2212 materials, and analyse in detail the effects of taking different criteria for the definition of the Fermi surface - all based upon the same, high resolution ARPES datasets. Our data show, for example, the presence of a shadow Fermi surface, as first seen by Aebi et al., with unprecedented clarity.
Thanks for financial support to: BMBF (05SB8 BDA6), DFG (Graduiertenkolleg 'Struktur- und Korrelationseffekte in Festkoerpern').
4PO4-16 Electronlike Fermi Surface in Bismuth Cuprates Determined by ARPES
A.A. Zakharov 1, T. Balasubramanian 1, M. Leandersson 2, A. Matsuura 2, and I. Lindau 2. 1 Max-Lab, Lund Univ.,Box 118, S-22100, Lund, Sweden. 2 Dept.of Synch.Rad. Res., Lund University, S-22100, Box 118, Lund, Sweden.
Presenting Author: A.A. Zakharov
We report an extensive angle-resolved photoemission spectroscopy study of a set of quickly dispersing electronic states near the G(0,0) point in Bi2212 single crystals at photon energy 38 eV. These states cross the Fermi surface along both the G-M and G-Y directions and are outside the well-known large Fermi surface and superstructure which occur in Bi2212. The electronic states have a strong nonmonotonic photon energy dependence and demonstrate a symmetry different from the symmetry of the Cu-O plane. The possible origin of these electronic states is discussed. In addition, we show that the whole Fermi surface topology in Bi2212 is photon energy dependent.
4PO4-17 ARPES lineshape of novel superconductors
Hong Ding 1, Jan Engelbrecht 1, Shancai Wang 1, Hongbo Yang 1, Hongbo Zhao 1, Robert Rogan 1, Juan-Carlos Campuzano 2, Adam Kaminski 2, Mike R. Norman 3, Takashi Takahashi 4, Takafumi Sato 4, K. Kadowaki 5, and Y. Maeno 6. 1 Physics Dept., Boston College. 2 Univ. of Illinois at Chicago. 3 Argonne Nat'l Lab. 4 Tohoku Univ. 5 Univ. of Tsukuba. 6 Hiroshima Univ.
Presenting Author: H. Ding
We report lineshape analysis of angle-resolve photoemission spectroscopy (ARPES) results on a high temperature superconductor - Bi2212 and a novel superconductor - Sr214. ARPES lineshape of these materials has a strong dependence of doping, temperature and momentum.
4PO4-18 Difference between microscopic and effective overlaps in the copper-oxide plains of high-Tc superconductors
Ladislav Jankovic and Denis K. Sunko, Department of Physics, Faculty of Science, University of Zagreb, Bijenicka cesta 32, HR-10000 Zagreb, Croatia
Presenting Author: D.K. Sunko
We investigate parametrizations required to reproduce observed Fermi surfaces of overdoped and slightly underdoped LSCO in two different models. One model is the standard three-band saddle-point slave boson with infinite repulsion on the coppers. The other is a model of CuO4 'molecules' randomly tiled in the plane, emphasizing the distinction between the local overlap, which is always the full (bare) one, and the effective overlap, connected with the reduced bandwidth due to the random tiling. In both models, the bare parameters are the copper-oxygen splitting, copper-oxygen overlap, and direct oxygen-oxygen overlap.
The slave-boson and random-tiling models behave similarly for overdoping, but differently for underdoping. While both models are able to reproduce the observed Fermi surfaces of the overdoped (x=0.3) compound at similar values of the bare parameters, the slave-boson model requires twice as large values of the bare oxygen-oxygen overlap to reproduce the experimental data for the underdoped (x=0.1) compound.
We conclude that keeping track of the difference between short-range and effective overlaps is physically significant for underdoped, but not for overdoped LSCO. This is consistent with the observed open Fermi surface at x=0.1 being due to correlation effects, and not to a large intrinsic oxygen-oxygen overlap.
4PO4-19 Electronic structure and energy gap of Nd1.85Ce0.15CuO4: evidence for disparity between hole and electron doped cuprate superconductors
N.P. Armitage 1, D.H. Lu 1, C. Kim 1, A. Damascelli 1, K.M. Shen 1, F. Ronning 1, Y. Onose 2, Y. Taguchi 2, Y. Tokura 2, and Z.-X. Shen 1. 1 Department of Physics, Applied Physics, and Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305, USA. 2 Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan.
Presenting Author: N.P. Armitage
The high-temperature superconductors are known to be doped Mott insulators. The symmetry or lack of it between doping with electrons or holes has important implications on theoretical models as many of them implicitly assume symmetry. Most of what we know about high-Tc superconductors comes from the p-type materials. However, the limited experiments that have been done on the n-types suggest that there is a real difference between the two sides of the phase diagram. Angle Resolved PhotoElectron Spectroscopy (ARPES) has provided important insight into the high-Tc problem, including the direct imaging of the anisotropic superconducting gap in the hole doped cuprates. Similar studies in the n-type material have not been possible thus far due to their smaller energy gap. However, recent advances in ARPES technology is making previously impossible measurements a reality. Ultra-high resolution ARPES was performed at the newly commissioned beamline 5-4 of the Stanford Synchrotron Radiation Laboratory on the n-type cuprate superconductor Nd1.85Ce0.15CuO4. Evidence is found for two distinct components in the near Ef electronic structure that contrasts strongly with that of the p-type. While one component retains much of the properties of the undoped insulator, the other component is metallic and near the Fermi energy. Moreover, we do not see the remarkable anisotropic leading edge gap that is the hallmark of d-wave superconductivity seen in the p-type superconductors. These distinct differences in electronic structure strengthen the case for an asymmetry between electron and hole doping.