A theory of thermal transport in a two-channel Kondo system, such as the one formed by a small quantum dot coupled to two leads and to a larger dot, is formulated. The interplay of the two screening constants allows an exploration of the Fermi liquid and non-Fermi liquid regimes. By using analytical, as well as numerical renormalization group methods, we study the temperature dependence of the thermal conductance and the Lorentz number. We find that in the low-temperature limit, the Lorentz number attains its universal value, irrespective of the nature of the ground state.

We use the numerical renormalization group method to investigate the spectral properties of a singleimpurity Anderson model with a gap ␦ across the Fermi level in the conduction-electron spectrum. For any finite ␦ Ͼ 0, at half filling the ground state of the system is always a doublet. Away from half filling a quantum phase transition ͑QPT͒ occurs as function of the gap value ␦, and the system evolves from the strong-coupling ͑SC͒ Kondo-type state, corresponding to ␦ Ͻ ␦ C toward a localized moment ͑LM͒ regime for ␦ Ͼ ␦ C . The opening of the gap leads to the formation of one ͑two͒ bound states when the system is in the SC ͑LM͒ regime. The evolution across the QPT of their positions and the corresponding weights together with the dynamic properties of the model are investigated.

Abstract. We consider the SU(3) attractive Anderson model, which can be realized in a triple-dot system, coupled to external leads that support chiral edge modes, and study its spectral and transport properties using the renormalization group approach. At the symmetric point, where the average occupation is n = 3/2, a resonance develops in the spectral functions, which differs significantly from the regular Kondo effect, and corresponds to trionic processes between states with zero and triple occupation of the dot system.