Capacitive coupling induced Kondo-Fano interference in side-coupled double quantum dots

We report capacitive coupling induced Kondo-Fano (K-F) interference in a double quantum dot (DQD) by systematically investigating its low-temperature properties on the basis of hierarchical equations of motion evaluations. We show that the interdot capacitive coupling U₁₂ splits the singly-occupied (S-O) state in quantum dot 1 (QD1) into three quasi-particle substates: the unshifted S-O₀ substate, and elevated S-O₁ and S-O₂. As U₁₂ increases, S-O₂ and S-O₁ successively cross through the Kondo resonance state at the Fermi level (ω=0), resulting in the so-called Kondo-I (KI), K-F, and Kondo-II (KII) regimes. While both the KI and KII regimes have the conventional Kondo resonance properties, remarkable Kondo-Fano interference features are shown in the K-F regime. In the view of scattering, we propose that the phase shift η(ω) is suitable for analysis of the Kondo-Fano interference. We present a general approach for calculating η(ω) and applying it to the DQD in the K-F regime where the two maxima of η(ω=0) characterize the interferences between the Kondo resonance state and S-O₂ and S-O₁ substates, respectively.