| In this talk, I will present a dissipative quantum phase transition in a relatively simple quantum impurity model. We study a spinless level that hybridizes with a fermionic band and is also coupled via its charge to a dissipative bosonic bath. We consider the general case of a power-law hybridization function Γ() ∝ ||r with r ≥ 0, and a bosonic bath spectral function B() ∝s with s ≥ -1. For r<1 and max(0,2r-1) < s < 1, this Bose-Fermi quantum impurity model features a continuous zero-temperature transition between a delocalized phase, with tunneling between the impurity level and the band, and a localized phase, in which dissipation suppresses tunneling in the low-energy limit. The phase diagram and the critical behavior of the model are elucidated using perturbative and numerical renormalization-group techniques, between which there is excellent agreement in the appropriate regimes. For r=0 this model's critical properties coincide with those of the spin-boson and Ising Bose-Fermi Kondo models, as expected from bosonization. Relevance of our model to mesoscopic experiments is discussed. |
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