Valence fluctuations in a lattice of magnetic molecules: Application to iron(II) phtalocyanine molecules on Au(111)

¹ Centro Atómico Bariloche and Instituto Balseiro, Comisión Nacional de Energía Atómica 8400 Bariloche, Argentina
² Instituto de Física de Rosario, Universidad Nacional de Rosario Bv. 27 de Febrero 210 bis, 2000 Rosario, Argentina

Received: 7 November 2014
Accepted: 30 January 2015

Abstract

We study theoretically a square lattice of the organometallic Kondo adsorbate iron(II) phtalocyanine (FePc) deposited on top of Au(111), motivated by recent scanning tunneling microscopy experiments. We describe the system by means of an effective Hubbard-Anderson model, where each molecule has degenerate effective d-orbitals with xz and yz symmetry, which we solve for arbitrary occupation and arbitrary on-site repulsion U. To that end, we introduce a generalized slave-boson mean-field approximation (SBMFA) which correctly describes both the non-interacting limit (NIL) U = 0 and the strongly interacting limit , where our formalism reproduces the correct value of the Kondo temperature for an isolated FePc molecule. Our results indicate that while the isolated molecule can be described by an SU(4) Anderson model in the Kondo regime, the case of the square lattice corresponds to the intermediate-valence regime, with a total occupation of nearly 1.65 holes in the FePc molecular orbitals. Our results have important implications for the physical interpretation of the experiment.