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TT: Fachverband Tiefe Temperaturen
TT 56: Correlated Electrons: Quantum-Critical Phenomena – Theory
TT 56.12: Vortrag
Mittwoch, 18. März 2015, 12:30–12:45, A 053
Selfconsistent Renormalization Group for Kondo Breakdown in Kondo lattice or Multi-Impurity Systems — •Ammar Nejati, Katinka Ballmann, and Johann Kroha — Universität Bonn
The conditions for breakdown of Kondo quasiparticles near a heavy-fermion quantum phase transition are still a controversial issue. We present a renormalization group (RG) theory for the breakdown of Kondo screening in multi-impurity Kondo systems without direct interimpurity dipole coupling, without pre-assumptions about magnetic ordering or Fermi surface criticality. Kondo singlet formation is signalled by the RG divergence of the conduction electron – local Kondo spin vertex Γ at the Kondo scale TK. In a multi-impurity system, Γ acquires a non-local, RKKY-mediated contribution from conduction electrons scattering at surrounding Kondo sites, which depends on the dynamical, local spin response χ on those sites. Because of its inverse dependence on TK at low energies, χ = (gµB)2/TK, the β−function depends parametrically on the Kondo scale in a selfconsistent way. As a result, we find a universal suppression of the Kondo scale TK(y) in Kondo lattice and multi-impurity systems, depending on a dimensionless RKKY coupling parameter y. Local Kondo screening is predicted to break down at a maximum RKKY coupling ymax, where ymax is a universal function of the bare TK(0). At the breakdown point, the TK-suppression assumes the universal value TK(ymax)/TK(0)=1/e≈ 0.368, in remarkable quantitative agreement with STM spectroscopy on two-impurity systems [1].
[1] J. Bork et al., Nature Physics 7, 901 (2011).