Spin-boson coupling in continuous-time quantum Monte Carlo

TL;DR

This paper applies continuous-time quantum Monte Carlo to the spin-boson coupling in the Bose Kondo model, revealing residual moments, hidden critical behavior, and a quantum critical point unaffected by bosonic fluctuations.

Contribution

It introduces a method to study spin-boson coupling in the Bose Kondo model using continuous-time quantum Monte Carlo, uncovering new critical phenomena and phase transition details.

Findings

Identification of residual moments and hidden critical behavior.

Observation of a quantum critical point between local-moment and Kondo singlet states.

Energy scale of bosonic fluctuations remains unaffected by the quantum phase transition.

Abstract

A vector bosonic field coupled to the electronic spin is treated by means of the continuous-time quantum Monte Carlo method. In the Bose Kondo model with a sub-Ohmic density of states $\rho_{B}(\omega) \propto \omega^{s}$ with s=0.2, two contributions to the spin susceptibility, the Curie term T^{-1} and the term T^{-s} due to bosonic fluctuations, are observed separately. This result indicates the existence of a residual moment and a hidden critical behavior. By including hybridization with itinerant electrons, a quantum critical point is identified between this local-moment state and the Kondo singlet state. It is demonstrated that the energy scale of the bosonic fluctuations is not affected by the quantum phase transition.