# Dresden 2020 – wissenschaftliches Programm

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# TT: Fachverband Tiefe Temperaturen

## TT 59: Correlated Electrons: Quantum Impurities and Kondo Physics; Other Materials

### TT 59.3: Vortrag

### Donnerstag, 19. März 2020, 15:30–15:45, HSZ 03

Genuine RKKY-Kondo quantum phase transition — •Krzysztof P. Wójcik^{1,2} and Johann Kroha^{1} — ^{1}Physikalisches Institut, Universität Bonn, Germany — ^{2}Institute of Molecular Physics, Polish Academy of Sciences, Poznań, Poland

Since the seminal papers of Jones and Varma, the RKKY interaction (Y) between two Kondo impurities is conventionally modeled by a Heisenberg coupling term. It gives rise to a quantum phase transition (QPT) between the Kondo and the RKKY phases in the two-impurity Kondo model. Yet, the significance of this result is still controversial. Firstly, the QPT is extremely fragile to particle-hole (PH) asymmetry, changing the QPT to a crossover in its presence. This has lead to the common belief that it cannot be realized in a realistic 2-impurity system and has made its relevance for lattice models debatable. Moreover, in the model Y and the Kondo exchange J are considered independent, although Y is genuinely generated by J, and the Kondo temperature depends on Y, as has been shown experimentally [1] and theoretically [2]. Recently, it has been proven that the QPT can be restored for weaker PH symmetry by parameter fine-tuning [3]. We revisit the problem to show by numerical renormalization group calculations that in the geometry of [1], Y induced solely by J causes the QPT for a properly symmetric case. We also discuss potential consequences of our findings for the lattice model in the context of "Kondo destruction".

[1] J. Bork et al., Nat. Phys. 7, 901 (2011).

[2] A. Nejati, K. Ballmann, J. Kroha, PRL 118, 117204 (2017).

[3] F. Eickhoff, B. Lechtenberg, F. Anders, PRB 98, 115103 (2018).