Interação elétron-fônon e efeito Kondo em impurezas quânticas multiorbitais

Abstract

In this we study the interplay between strong electron-electron and electron-phonon interactions in a two-orbital molecule coupled to metallic contacts, in the low-temperature regime. The electronelectron and electron-phonon interactions are incorporated by mean of a Coulomb interaction term and a Holstein-like coupling of phonons to the molecular occupancies, respectively. Moreover, for a more complete description of the electron-phonon interaction, we introduce an additional term accounting for a phonon-mediated interorbital tunneling. By combining canonical transformations with nonperturbative numerical renormalization-group calculations, we obtain a comprehensive description of the system s many-body physics in the anti-adiabatic regime, where the phonons adjust rapidly to changes in the orbital occupancies, and are thereby able to strongly affect the Kondo physics. The electron-phonon interactions strongly modify the bare orbital energies and the Coulomb repulsion between electrons in the molecule, and tend to inhibit tunneling of electrons between the molecule and the leads. The consequences of these effects are considerably more pronounced when both molecular orbitals lie near the Fermi energy of the contacts than when only one orbital is active. In situations where a local magnetic moment forms in the molecule, there is a crossover with increasing electronphonon coupling from a regime of collective Kondo screening of the moment to a limit where the supression of the moment is dominated by the interaction of the electrons with local phonons. At low temperatures, this crossover is associated with a rapid increase of the electronic occupancy of the molecule as well as with a marked drop in the linear electrical conductance through the single-molecule junction.