Interference and interaction effects in multi-level quantum dots

Using renormalization group techniques, we study spectral and transport properties of a spinless interacting quantum dot consisting of two levels coupled to metallic reservoirs. For strong Coulomb repulsion $U$ and an applied Aharonov-Bohm phase $\varphi$, we find a large direct tunnel splitting $\mathrm{\mid }\mathrm{\Delta }\mathrm{\mid }\sim (\mathrm{\Gamma }\mathrm{/}\pi )\mathrm{\mid }\cos (\varphi \mathrm{/}2)\mathrm{\mid }\ln (U\mathrm{/}{\omega }_c)$ between the levels of the order of the level broadening $\mathrm{\Gamma }$. As a consequence we discover a many-body resonance in the spectral density that can be measured via the absorption power. Furthermore, for $\varphi =\pi$, we show that the system can be tuned into an effective Anderson model with spin-dependent tunneling.