First-Principles Angle-Resolved Photoemission Intensity Calculations in Y Ba 2 Cu 3 O 7
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FIRST-PRINCIPLES ANGLE-RESOLVED PHOTOEMISSION INTENSITY CALCULATIONS IN YBa 2 CUs07 34 1 12 M. Lindroos ' , A. Bansil and J. C. Campuzano ' 1 Physics Department, Northeastern University, Boston, Massachusetts 02115 2 Physics Department, Tampere University of Technology, Tampere, Finland 3 Materials Science Division, Argonne National Laboratory,nllinois 60439 t Dept. of Physics, University of Illinois at Chicago,Illinois 60860
ABSTRACT We discuss the application of the multiple scattering theory to obtain first-principles predictions of angle-resolved photoemission intensities (ARPES) in the high-T, superconductors. In this connection, we have generalized and implemented the 'one-step' pho-
toemission approach to treat systems with an arbitrary number of atoms in the layer unit cell. We illustrate the methodology with results for the r-S symmetry direction for the (001)-surface of orthorhombic YBa 2CusO7 . Our computations give insight into the effects of surface termination, and of polarization of incident light on photoemission intensities. 1. INTRODUCTION The theoretical interpretation of the photoemission spectroscopy has generally proceeded at two levels of sophistication, the simpler of which involves the correlation of structures in the spectra with specific transitions in the bulk and surface bands [1,2]. The more difficult level involves an analysis of the observed spectral intensities [3,4,5]. Extensive experience reveals that photoemission is a very complex process, the spectra even in metals with simple lattice structures exhibit features from not only band-type transitions but also from many other processes, the spectra being further modulated by final state effects [6]. It is clear that a satisfactory understanding of the ARPES experiments requires direct comparisons between the measured intensities and the corresponding theoretical predictions. With this motivation, we have started an effort to obtain first-principles theoretical angle-resolved photoemission intensities for materials with complex crystal structures, in particular the high-T,'s, using the 'one step' formulation of Pendry [3]. In the one-step approach, which makes extensive use of the multiple scattering theory (MST) techniques, the photoemission process is treated as a single quantum mechanical event, and artificial distinctions between the processes of excitation, transport, and transmission of the electron through the surface barrier invoked in the earlier 'three step' type model are removed [4]. It is hoped that calculations of ARPES intensities in the high-T,'s will help identify spectral features which are well-described by the band theory, as well as those which are not. The ARPES line shapes play an important role in a number of recent discussions in the literature. For example, the detailed shapes of the ARPES spectral peaks
have been offered as evidence in support of a highly correlated picture of the electron gas in the high-T,'s [7]. Similarly, the energy dependence of the spectral widths has been argued to be consistent
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