Berry Phase and the Breakdown of the Quantum to Classical Mapping for the Quantum Critical Point of the Bose-Fermi Kondo model

TL;DR

This paper investigates how the Berry phase affects the quantum critical behavior in the Bose-Fermi Kondo model, revealing that including the Berry phase leads to an interacting fixed point and breaks the quantum-to-classical mapping.

Contribution

It demonstrates that the Berry phase term fundamentally alters the nature of the quantum critical point in the Bose-Fermi Kondo model, showing the importance of topological effects.

Findings

Neglecting the Berry phase yields a Gaussian fixed point.

Including the Berry phase results in an interacting fixed point.

The quantum-to-classical mapping breaks down when the Berry phase is considered.

Abstract

The phase diagram of the Bose-Fermi Kondo model contains an SU(2)-invariant Kondo-screened phase separated by a continuous quantum phase transition from a Kondo-destroyed local moment phase. We analyze the effect of the Berry phase term of the spin path integral on the quantum critical properties of this quantum impurity model. For a range of the power-law exponent characterizing the spectral density of the dissipative bosonic bath, neglecting the influence of the Berry phase term makes the fixed point Gaussian. For the same range of the spectral density exponent, incorporating the Berry phase term leads instead to an interacting fixed point, for which a quantum to classical mapping breaks down. Some general implications of our results are discussed.