R. Manzke

On the electronic structure and superconducting gap of Bi2Sr2CaCu2O8

Abstract Photoemission spectra taken at room temperature with high energy and angle resolution on Bi 2 Sr 2 CaCu 2 O 8 single crystals reveal a band near E F with weak dispersion along λX. It crosses E F at about 1/2 λX and the occupied part becomes visible up to the Brillouin zone boundary in angle-resolved inverse photoemission spectra. Starting for T>Tc with a clear Fermi edge, for T F to higher binding energy related to the opening of the superconducting gap of Δ=(30±4) meV. These findings strongly favour Fermi liquid based theories for high-Tc superconductivity in this material.

High-energy spectroscopy studies of high-Tc superconductors

Abstract High-energy spectroscopy studies of cuprate superconductors and their undoped parent compounds are reviewed. In particular, we report on investigations by electron energy-loss, x-ray absorption, and angle-resolved photoemission spectroscopy. Information on the character and the symmetry of states close to the Fermi level has been obtained by core level excitations. Angle-resolved photoemission spectra yield “bands” and the shape of the Fermi surface.

An intrinsic metallic surface state on Ge(001) 2 × 1

Abstract Photoemission studies with high angle and energy resolution are described which reveal a metallic dangling-bond surface state on Ge(001) 2 × 1 surfaces located in the fundamental energy gap. At the center of the surface Brillouin zone, this surface state is found closer to the Fermi level at 270 meV above the valence band maximum. This surface state shows a very pronounced dispersion around the zone center not explicable by calculations within the local density approximation. The energy position and dispersion of the surface state, which is intimately related to the surface dimer of the 2 × 1 reconstruction, is discussed in comparison with recent theoretical results.

Experimental surface band structure of CdTe(110)

Abstract Angle-resolved photoemission and constant-final-state (CFS) spectroscopy are performed with synchrotron radiation to determine the experimental surface band structure E ( k ∥ ) along the high symmetry lines ГX′MXГgG of in situ cleaved CdTe(110). In order t distinguish between surface and bulk related features we utilized the k ⊥ dispersion behaviour of surface states by photon energy dependent normal emission spectra and off-normal CFS spectra at several critical points of the surface Brillouin zone (BZ) as well as their particular k ∥ dispersion and polarization behaviour. Three surface states and one surface resonance are clearly identified, whereas the resonance is only visible in the second surface BZ. In particular, the energy position of the anion derived dangling bond state with respect to the bulk valence band maximum Γ 8 is determined. The surface band structure is compared with previous experimental and theoretical results.

Fermi-liquid-type spectral function and angle resolved photoelectron spectra of the Ti-3dz2-band of TiTe2

Angle and temperature dependent photoelectron spectra with high energy and momentum resolution (AE = 30meV, A0 < ~tO.5’) were taken near the Fermi energy (& < 1eV) of the quasi-two-dimensional, metallic layer compound TiTeg along the direction I%. The aim was to test the range of the validity of the Fermi liquid model using a Taylor expansion for the self-energy used by Claessen et al. [I] for a system whose low energy properties are those of a normal metal. Single crystalline samples have been prepared by vapor growth technique using different amounts of Te in order to influence the intercalation of surplus Ti. We found a dependence of the dispersion of the Ti-3d,a-derived band on the stoichiometry of the samples. For an exact line shape analysis the spectra were fitted by a least-squares-method to a Fermi-liquid-type spectral function taking into account the crucial effects due to the apparatus, as there are the energy resolution and finite angle resolution which leads to a limited integration in k-space. In the region where the Ti-3d,a-derived band crosses the Fermi level we found excellent agreement between the experimental line shape and the Fermi liquid model. On the other hand there are distinct deviations between the theoretical and the experimental line shape at the Brillouin zone boundary even for a self-energy proposed by Matho [2] without Taylor expansion.

Surface effects on YBa2Cu3O7−δ by angle-resolved photoemission

Abstract High-resolution angle-resolved photoemission performed on cleaved surfaces of twinned YBa 2 Cu 3 O 7−δ single crystals at 20 K revealed an intrinsic surface-derived electronic state for this high-temperature superconductor. In the spectra it is very pronounced around the X(Y) point of the Brillouin zone where its binding energy is 0.92 eV. It shows slight k ∥ -, no k ⊥-dispersion , and a strong sensitivity to surface contamination. The existence of this state points to a rearrangement of electron charge in the surface layers and consequences for the superconducting behaviour on the surface of 1:2:3 superconductors will be discussed.

Surface band structure of CdTe(111)-2 × 2 by angle-resolved photoemission

Abstract The surface band structure of non-cleavable CdTe(111)-2 × 2 reconstructed surfaces is determined by means of angle-resolved photoemission and constant-final-state (CFS) spectroscopy. The experiments were performed with He I radiation and synchrotron radiation from the DORIS II storage ring at HASYLAB. High-quality (111)-2 × 2 surfaces were prepared by sputtering and annealing controlled by electron diffraction (LEED and RHEED). In order to distinguish between surface and bulk related emissions in the spectra we utilized, besides the criteria that the k ∥ dispersion of surface states should reveal the 2 × 2 periodicity of the surfac mesh, also photon energy dependent CFS series at several critical points of the surface Brillouin zone. The data on CdTe(111) will be compared with experimental and theoretical results which are available for the electronically similar GaAs(111) surface.

Angle resolved resonant photoemission spectra of GaAs(110)

Abstract Off normal resonant photoemission originating from the decay of a surface core exciton on GaAs(110) studied with high angle resolution shows spectra of complex fine structure, concerning the relative contributions of surface or bulk states, resonance or anti-resonance of the particular states or the strength of their resonant enhancement. In conjunction with theory this leads to a more refined view of several aspects of resonant photoemission and its usual interpretation in oversimplified terms. The k -resolved resonant current at critical points of the surface Brillouin zone was calculated, starting from first principle scattering theory, and good correspondence with the experimental spectra was found, thereby confirming the theoretical model.

The surface band gaps of Ge(001)2×1

Abstract Applying in-situ combination of angle-resolved photoemission and inverse photoemission spectroscopy on clean Ge(001)2×1 surfaces we determined the binding energies of occupied and unoccupied surface states associated with the surface dimer of the 2×1 reconstruction at the high symmetric points, Γ , J , J ′, 1 2 J K and K of the surface Brillouin zone. Together with the experimentally determined valence band maximum the results will be compared on an absolute energy scale with recent surface band structure calculations.

Investigations of the electronic structure of cuprate superconductors by high-energy spectroscopy

Abstract Studies of the electronic structure of high-Tc superconductors and related compounds by high-energy spectroscopies are reviewed. In particular, we report on investigations by electron energy-loss, angle-resolved photoemission, and inverse angle-resolved photoemission spectroscopy.