* Corresponding author. Tel.: 34-93-581-1353; fax: 34-93-581- 1350; e-mail: toni@elema.uab.es. Physica B 259 — 261 (1999) 940—941 Quasiparticle structure of Sr RuO A. Pe´rez-Navarro*, J. Costa-Quintana, F. Lo´pez-Aguilar Grup d ’Electromagnetisme, Cn, Universitat Auto % noma de Barcelona, E-08193, Bellaterra, Barcelona, Spain Abstract The non-copper layered perovskite, Sr RuO , is expected to be a very useful reference material for interpreting experiments on the high ¹ cuprate superconductors. A band structure calculation for Sr RuO is performed. Starting from the electronic structure determined in the local density formalism, the Dyson’s equation with self-energies arising from the Hubbard hamiltonian is solved by diagonaliz- ing the Green’s function in k-space. The density of states is obtained by considering the renormalization factor and the life-times of the quasiparticle states in each pole of the interacting system. This leads to modification of the density of states calculated in the local density formalism, and the results fit experimental data not only in the position of peaks, but also in their intensity and in the number of states at Fermi level. 1999 Elsevier Science B.V. All rights reserved. Keywords: Sr RuO ; Hubbard’s self-energy; Electronic structure Since their discovery in 1986 all high-¹ superconduc- tors that have been characterized contain CuO planes. In 1994, a noncuprate perovskite, Sr RuO , was dis- coverd which had a transition temperature of 0.93 K [1]. What makes this compound interesting is that it presents the same crystal structure as La CuO . The role played by CuO planes in cuprates is played by RuO in the ruthenate [2]. Experimentally, it seams clear that correlation effects are important for Sr RuO [1,3,4], but they have not still been included in any theoretical density of states (DOS) calculation [5,6]. These works fit recent X-ray fluores- cence emission studies for p orbitals of oxygen, but not for d orbitals [7]. We calculate the band structure of Sr RuO by the symmetrized augmented plane wave method in the local density approximation (LDA). Our calculations fit ex- perimental results [8] as well as Refs. [5,6]. In Fig. 1a the DOS is shown with a quite different structure from that obtained experimentally in Ref. [3] or Ref. [9]. In fact, this last one is capable of differentiating a three peaks structure that Ref. [3] cannot. In our results we see a central peak a little above the Fermi level that is experimentally found below this level. We think that the origin of this problem is the non-inclusion of correlation effects in d orbitals. In order to take into account these correlations we diagonalize the Green’s function in k-space [10,11], with a self-energy obtained with the random phase approxi- mation [12]: ()"! ºf 2 1 n # #!i # 1!n ! !!i # 1 n # #!i # 1!n ! !!i , (1) where º is the Coulomb correlation, f" 2gn(1!n), "g!ºf and "g#ºf are the plas- mon frequencies, g"(#)!i(#), and , and 0921-4526/99/$ — see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 8 ) 0 1 0 9 7 - 7