Zero-field splitting of the Kondo resonance and quantum criticality in triple quantum dots.

Magnetic fields are known to be detrimental to the Kondo effect. In quantum dots (QDs), this is signaled by the splitting of the Kondo resonance (KR). However, zero-field splitting of the KR is predicted to occur in T-shaped QDs, where the hanging dot is within the Kondo regime and the second dot behaves as a resonant noninteracting level [1]. In this work we use the numerical renormalization group method to study a triple QD system in which two effective noninteracting dots are connected in parallel to metallic leads, as well to a third interacting dot. In absence of external fields, the fine tuning of the noninteracting levels causes a splitting of the KR, in such a way that the spectral function of the interacting dot vanishes at the Fermi level, without undermining the Kondo correlations. In addition, the system can be tuned to a pseudogap regime, which presents a competition between the Fano-Kondo effect and a quantum phase transition of the Kosterlitz-Thouless type. Signatures of these behaviors can be experimentally studied through conductance measurements [2].
[1] L. G. G. V. Dias da Silva et al., PRL 97, 096603 (2006).
[2] Arturo Wong and Francisco Mireles, PRB 94, 245408 (2016).