POSTER SESSION 4PO4: ARPES and Fermi Surface

Thursday, Feb. 24, 1:45 p.m. – 3:45 p.m., Hall D (GRB)

4PO4-1 Remnant Fermi Surfaces in Cuprates

Cristian Kusko and Robert S. Markiewicz, Physics Dept., Northeastern Univ., Boston, MA 02115

Presenting Author: C. Kusko

We investigate a new methodology proposed by Ronning et al. for analysing the angle resolved photoemission data on high T_c cuprates - the remnant Fermi surface (rFs). This is the locus of the points in k-space where the momentum distribution n(k) is one half, and can be determined even in strongly correlated electron systems that lack the Fermi surface. There are two fundamentally diferent classes of remnant Fermi surfaces depending on whether the interaction leads to pairing or to a generalized nesting (magnetic or charge) instability. For pairing the remnant Fermi surface follows faithfully the Fermi surface, whereas for magnetic or charge instabilities the rFs maps the corresponding superlattice Brillouin zone. We exemplify these concepts by determining the rFs for a particular model presenting two competing phases: flux phase (nesting) and d-wave superconductivity (pairing) mapping the evolution of rFs with dopping and temperature.

4PO4-2 Momentum and energy dependance of scattering rate in high T_c superconductors studied by ultrahigh momentum resolution ARPES

Adam Kiminski 1, Helen Fretwell 2, Joel Mesot 3, Juan Campuzano 1, Mike R. Norman 4, Mohit Randeria 5, Takafumi Sato 6, Takashi Takahashi 6, Kazuo Kadowaki 7, and Takashi Mochiku 8. 1 Physics Dept., University of Illinois at Chicago, Argonne; National Laboratory. 2 University of Wales, Swansea. 3 Laboratory for Neutron Scattering, ETH Zurich & Paul Scherrer Institute. 4 Argonne National Laboratory. 5 Tata Institute of Fundamental Research, Mumbai. 6 Tohoku University, Sendai. 7 Institute of Materials Science, University of Tsukuba. 8 National Research Institute for Metals, Sengen, Tsukuba.

Presenting Author: A. Kaminski

In this paper we study the momentum and energy dependence of the scattering rate in high T_c superconductors using ultrahigh momentum resolution ARPES. By improving momentum resolution we are able to obtain scattering rate information at all points on the Fermi Surface, including the highly dispersive nodal region.

In the optimally doped compounds, we find Fermi liquid like behavior along the whole Fermi surface but only in superconducting state at low temperatures. In the normal state we find that the scattering rate has Marginal Fermi Liquid-like behavior. We compare our data with Green's function simulations in order to obtain accurate information about the self-energy. This allows us to make direct comparisons of ARPES data to various transport measurements.

Implications of these recent results for different models of the mechanism of the high temperature supercunductivity will be discussed.

4PO4-3 The interplay between flattening and damping of single particle spectra in strongly correlated Fermi systems

Victor Khodel and Mikhail Zverev, Kurchatov Institute, Kurchatov square 1, 123182 Moscow, Russia

Presenting Author: V. Khodel

The flattening of the single particle electron spectra in crystals is analysed within the fermion condensation model. Spin fluctuations are shown to further the formation of the fermion condensate in the vicinity of the Van Hove points. The interplay between the flattening and the damping of the single particle spectra at extremely low temperature is investigated. The widths of the single particle states outside the regions occupied by the fermion condensate (patches) are found to grow up linearly with energy over a wide region of it as in a marginal Fermi liquid while the linewidth of the fermion condensate states has more complicated form. The results of the analysis are compared with those obtained within alternative models and with available experimental data.

4PO4-4 Angle-resolved photoemission in doped cuprates and other charge-transfer Mott insulators

Chris J. Dent, Theory Group, Department of Physics, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom, and Alexandre S. Alexandrov, Department of Physics, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom

Presenting Author: C.J. Dent

A theory of angle-resolved photoemission (ARPES) in doped cuprates and other charge-transfer Mott insulators is developed taking into account the realistic (LDA+U) band structure, (bi)polaron formation due to the strong electron-phonon interaction, and a random field potential. In most of these materials the first band to be doped is the oxygen band inside the Mott-Hubbard gap. We derive the coherent part of the ARPES spectra with the oxygen hole spectral function calculated in the non-crossing (ladder) approximation and with the exact spectral function of a one-dimensional hole in a random potential. Some unusual features of ARPES including the polarisation dependence and spectral shape in Y123 and Y124 are described without any Fermi-surface, large or small. The theory is compatible with the doping dependence of kinetic and thermodynamic properties of cuprates as well as with the d-wave symmetry of the superconducting order parameter.

4PO4-5 Angle-resolved Photoemission Studies on YBa₂Cu₄O₈ Single Crystals

Donghui Lu 1, Norman P. Armitage 2, Zhi-xun Shen 3, Kiminori Waku 4, and Hidenori Takagi 5. 1 Center for Material Research, Stanford University, Stanford CA 94305. 2 Deparment of Physics, Stanford University, Stanford CA 94305. 3 Deparment of Physics and Applied Physics, Stanford University, Stanford CA 94305. 4 Insitute for Solid State Physics, University of Tokyo, Tokyo 106-8666, Japan. 5 Department of Chemistry and Insitute for Solid State Physics, University of Tokyo, Tokyo 106-8666, Japan.

Presenting Author: D.H. Lu

We report high-resolution angle-resolved photoemission studies on the {001} surface of YBa₂Cu₄O₈ single crystals. Polarization dependent band dispersions in the near EF region are presented along high symmetry lines in the Brillouin zone. The data are compared with previous angle-resolved photoemission results on the untwinned YBa₂Cu₃O_6.95.

*4PO4-6 Superconducting gap, Pseudogap, and Fermi surface of Bi2201: high energy- and momentum-resolution photoemission study

T. Sato 1, Y. Naitoh 1, T. Kamiyama 1, T. Takahashi 1, T. Yokoya 2, J. Mesot 3,4, A. Kaminski 3,4, H. Fretwell 3,4, J.C. Campuzano 3,4, H. Ding 5, I. Chong 6, T. Terashima 6, M. Takano 6, and K. Kadowaki 7. 1 Department of Physics, Tohoku University, Sendai 980-8578, Japan. 2 Institute of Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan. 3 Department of Physics, Univerisity of Illinois at Chicago, Chicago, IL 60607. 4 Materials Science Division, Argonne National Laboratory, Argonne, IL 60439. 5 Department of Physics, Boston College, Chestnut Hill, MA 02467. 6 Institute for Chemical Research, Kyoto University, Uji 611-0011, Japan. 7 Institute of Materials Science, University of Tsukuba, Ibaraki 305-3573, Japan.

Presenting Author: T. Sato

We have performed a systematic high energy (7 meV) and momentum (0.01A-1) resolved ARPES study on Bi₂Sr₂CuO₆ (Bi2201) with various dopings (T_c= underdope 18K, 19K, optimally dope 22K, and overdope 17K, 0K). All the samples show a large hole-like Fermi surface centered at X point and the volume exhibits a systematic evolution with doping.

Superconducting gap of a few meV is seen on the Fermi surface near the (p,0) point at low temperature, suggesting the d_x2-y2 symmetry. The size of superconducting gap increases with less doping, indicating the stronger pairing interaction in the underdoped region. Temperature-dependent measurement shows that a pseudogap exists above T_c for underdoped samples. We found that the size of both superconducting- and pseudo-gaps is well scaled with the maximum T_c of the sample irrespective with the number of CuO₂ layers in the crystal. This indicates that the pseudogap in Bi2201 is pairing origin as in Bi2212, and the energy scale of the pseudogap is characterised by the strength of pairing interaction.

4PO4-7 Polarization and doping effects in high resolved ARPES and XAS spectra on n=1 Bi₂Sr_2-xLa_xCuO_6+d - single crystals

R. Muller, C. Janowitz, A. Krapf, H. Dwelk, and R. Manzke, Humboldt-Universitat zu Berlin, Institut fur Physik, Invalidenstr. 110, D-10115 Berlin, Germany

Presenting Author: R. Muller

The resolution of Electronic states in the vicinity of the Fermi energy of most commonly studied HT_c-superconductors like e.g. Bi₂Sr₂CaCu₂O₈ in the non-superconducting state depends on a number of parameters such as angular and energy resolution, temperature, and the polarization of the impinging radiation. The occurence of shadow and umklapp bands yields replicas of the Fermi surface. Besides sample quality leading to scattering and therewith broadening furthermore the magnitude of the bilayer splitting for n=2 compounds is not quantitatively accessible, since no such splitting has been resolved yet.

In the case of Bi₂Sr_2-xLa_xCuO_6+d with different doping levels and only one CuO₂ layer per unit cell a number of these parameters can be controlled in a way that the intrinsic linewidth and dispersion can be determined more unequivocally. In this contribution we investigate the Fermi surface of n=1 material at various photon energies and polarization geometries by high resolution photoemission and discuss apparent lineshape changes. Special emphasis is set on the k-space region around the M point. Additional polarization dependent XAS-measurements were performed for the unfilled states.

*4PO4-8 A reexamination of the electronic structure of Bi-Sr-Ca-Cu-O: an electron-like Fermi Surface and absence of flat band at EF

Y.-D. Chuang 1, A.D. Gromko 1, D.S. Dessau 1, Y. Aiura 2, Y. Yamaguchi 2, K. Oka 2, A.J. Arko 3, J. Joyce 3, H. Eisaki 4, S.I. Uchida 4, K. Nakamura 5, and Y. Ando 5. 1 Dept of Physics, University of Colorado, Boulder, CO 80309-0390. 2 Electrotechnical Laboratory (ETL),1-1-4 Umezono, Tsukuba, Ibaraki 305, Japan. 3 Los Alamos National Laboratory, Los Alamos, NM 87545. 4 Dept. of Superconductivity, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan. 5 Central Research Institute of Electric Power Industry (CRIEPI), 2-11-1 Iwato-Kita, Komae, Tokyo 201-8511, Japan.

Presenting Author: Y.-D. Chuang

We present a re-examination of the electronic structure and Fermi Surface (FS) of Bi-Sr-Ca-Cu-O as obtained from angle-resolved photoemission experiments. By applying a stricter set of FS crossing criteria as well as by varying the incident photon energy outside the usual range around 22eV, we have found a very different behavior from that previously observed. We have found an electron-pocket portion of FS centered around zone center and the flat bands near M are absent. These results are robust over large range of doping and from single to double layer material.

4PO4-9 Quasiparticles along the (p ,p ) direction in the SC state of Bi2212

J. Mesot 1, A. Kaminski 2, H. Fretwell 2, J.C. Campuzano 2, H. Ding 3, M.R. Norman 4, M. Randeria 5, T. Sato 6, T. Takahashi 6, and K. Kadowaki 7. 1 Paul Scherrer Institute, CH-5304 Villigen PSI, Switzerland. 2 University of Illinois at Chicago, Chicago, IL 60607. 3 Boston College, Chestnut Hill, MA 02467. 4 Argonne National Laboratory, Argonne, IL 60439. 5 Tata Institute of Fundamental Research, Mumbai 400005, India. 6 Tohoku University, 980-8578 Sendai, Japan. 7 University of Tsukuba, Ibaraki 305, Japan.

Presenting Author: J.F. Mesot

We present recent high (momentum and energy) resolution ARPES experiments which lead to qualitatively new results on the spectra of Bi2212 along the (p ,p ) direction, where there is a node in the superconducting gap. Under such experimental conditions we now see the intrinsic lineshape, which indicates the presence of true quasiparticles at the Fermi momentum in the superconducting state, and lack thereof in the normal state. The region of momentum space probed here is relevant for charge transport, motivating a comparison of our results to conductivity measurements by infrared reflectivity.

*This work was supported by the Swiss National Science Foundation, DOE-BES, Contract W-31-109-ENG-38 and NSF-DMR 9624048 and 91-20000.