Quantum dot in a Aharonov-Bohm interferometer: magnetic flux-dependent pseudogap in the Kondo regime.

We study a quantum dot embedded in one of the arms of a Aharonov-Bohm interferometer threaded by a magnetic flux $\Phi$. In the regime where a single resonant mode propagates in the interferometer's ``free arm", the system can be described by an effective one-channel Anderson impurity model coupled to a non-constant, flux-dependent density of states (DoS). We present numerical renormalization-group results for the Kondo temperature $T_K$, phase shift and finite-temperature linear conductance. For $\Phi\neq 0$, the ground state of the system is Kondo-like, with a renormalized $T_K$. For $\Phi=0$, the effective DoS \textit{vanishes} at the Fermi energy and the system maps into the pseudogap Anderson model, which displays a quantum critical transition between Kondo and non-Kondo phases [1]. Signatures of these effects appear in the conductance and transmission phase-shifts across the system. This setup constitutes an experimental realization of a tunable pseudogap Anderson Hamiltonian, allowing for an experimental probe into the non-trivial properties of such a model. \newline [1] L.G.G.V. Dias da Silva et al, PRL {\bf 97} 096603 (2006). \newline Supported by NSF-IMC/NIRT.