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TT: Tiefe Temperaturen

TT 6: Postersitzung I (Amorphe- u. Tunnelsysteme, Niedrigdimensionale Systeme, Supraleitung: Elektronenstruktur, Phononen, Tunneln, Ordnungsparameter)

TT 6.30: Poster

Montag, 24. März 2003, 14:30–19:00, P2c, P2d

Unoccupied band structure of Bi2212 by very-low-energy electron diffraction: Origin of the final state effects in photoemission — •V.N. Strocov¹, R. Claessen¹, and P. Blaha² — ¹Experimentalphysik II, Universitaet Augsburg, D-86135 Augsburg, Germany (email F1XVS@fy.chalmers.se) — ²Institut fuer Materialchemie, Technische Universitaet Wien, A-1060 Wien, Austria

We present first direct data on the photoemission final states in Bi2212 in the energy interval from 5 to 50 eV relative to the Fermi level, achieved by very-low-energy electron diffraction (VLEED) with a support of full-potential DFT band structure calculations: 1) Energy positions, dispersions and lifetimes of the final states, which is of vital importance for predictive use of the matrix element effects for resolving details of the electronic structure such as bilayer splitting. Although the final states are essentially 3-dimensional, the escape depth is significantly reduced by admixture of 2-dimensional states. The lifetime decreases around 25 eV due to plasmon excitation; 2) A hidden c(2x2) periodicity observed in VLEED images below 20eV as intensity modulation of the incommensurate spots. Such a periodicity reveals either the AFM fluctuations in the CuO planes, or multiple scattering effects involving the CuO, SrO and BiO planes. In any case, it leads to significant extrinsic final-state diffraction contribution to the shadow Fermi surface intensity; (3) Energy dependence of the final-state diffraction effects as reflected in the I(V) dependences of the VLEED intensity.