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).