Regensburg 2013 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 48: Correlated Electrons: Quantum-Critical Phenomena - Theory
TT 48.4: Vortrag
Mittwoch, 13. März 2013, 17:45–18:00, H19
Kondo breakdown in RKKY-coupled two- and multi-impurity Kondo systems — •Ammar Nejati, Katinka Ballmann, and Johann Kroha — Universität Bonn
The driving mechanisms for magnetic quantum phase transitions in different heavy fermion systems have remained obscure. One difficulty is the lack of theoretical methods for treating a possible breakdown of
Kondo screening and of heavy quasiparticles without invoking magnetic order. We consider a dense system of Kondo impurities and develop a novel renormalization group technique for the local Kondo coupling Ji on a given impurity site i. At the one-loop level, the β function for Ji includes RKKY corrections due to the coupling to the surrounding
impurities j≠ i, which arises in order O(JiJj) from the local couplings Ji and Jj. In this way, double counting of RKKY operators is avoided. This method allows to determine the single-impurity Kondo screening scale TK(y) as a function of the dimensionless RKKY coupling y (determined alone by the conduction electron
response function), without invoking magnetic ordering fluctuations. The solution of the RG equation indicates a breakdown of Kondo screening when y exceeds a critical value yc, where the latter can be expressed in a universal way in terms of the bare Kondo temperature TK(y=0). For y<yc the RKKY-corrected single-impurity Kondo screening scale TK(y)/TK(0) is a universal
function of y/yc [1]. We compare these predictions with recent experiments on heavy fermion [1] and two-impurity [2] systems.
[1] M. Klein et al., PRL 101, 266404 (2008)
J. Bork et al., Nature Physics 7, 901 (2011)