Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 50: Symposium: Surface Spectroscopy on Kondo Systems II (Invited Speakers: Jonathan Denlinger, Johann Kroha, Alexander Schneider)
O 50.2: Hauptvortrag (ohne Erstattung)
Mittwoch, 27. Februar 2008, 15:45–16:15, HE 101
Local Kondo Physics vs. Lattice Effects in Real Solids — •Johann Kroha — Physikalisches Institut, Universität Bonn
In recent years, photoemission spectroscopy (PES) as well as scanning tunneling microscopy (STM) have been developed into powerful tools for investigating the low-energy features characteristic for strongly correlated impurity and lattice systems due to their high spectral resolution of only a few meV.
We first review briefly the physical origin of the multiple low-energy resonances in heavy-electron compounds as Kondo spin fluctuations, involving the crystal-field or spin-orbit split 4f orbitals of rare earth ions. We then discuss the different shape of STM Kondo spectra, where multiple Kondo resonances are not observed, and explain this fact by the orbital selectivity of the STM in contrast to PES. We propose a method to determine the spatial orientation of individal orbitals of Kondo impurities on a metal surface from their STM spectra.
In the second part of the talk we analyze theoretically recent PES experiments on the heavy fermion compound CeCu6−xAux, which undergoes a quantum phase transition (QPT) to an antiferromagnetically ordered state at x≃ 0.1. The PES spectra, taken at T≃ 10 K, i.e. well above the ordering temperature, probe the local Kondo physics of the Ce atoms, and indicate a sharp drop of the Kondo temperature TK near x=0.1. By analyzing the origin of this drop theoretically, we conjecture on whether in CeCu6−xAux the Hertz-Millis scenario (persistence of quasiparticles through the QPT) or the local quantum critical scenario (breakdown of quasiparticles at the QPT) is realized.