Kondo screening of a high-spin Nagaoka state in a triangular quantum dot

Abstract We study transport through a triangle triple quantum dot connected to two noninteracting leads using the numerical renormalization group (NRG). The triangle has a high-spin ground state of S = 1 caused by a Nagaoka ferromagnetism, when it is isolated and has one extra electron introduced into a half-filling. The results show that the conduction electrons screen the local moment via two separate stages with different energy scales. The half of the S = 1 is screened first by one of the channel degrees, and then at very low temperature the remaining half is fully screened to form a Kondo singlet. The transport is determined by two phase shifts for quasi-particles with even and odd parities, and then a two-terminal conductance in the series configuration is suppressed g series ≃ 0 , while plateau of a four-terminal parallel conductance reaches a unitary limit value g parallel ≃ 4 e 2 / h of two conducting modes.