title: Quantum phase transition in the sub-Ohmic spin-boson model: quantum Monte Carlo study with a continuous imaginary time cluster algorithm.
abstract: A continuous time cluster algorithm for two-level systems coupled to a dissipative bosonic bath is presented and applied to the sub-Ohmic spin-boson model. When the power s of the spectral function Jomega proportional, variant omegas is smaller than 1/2, the critical exponents are found to be classical, mean-field like. Potential sources for the discrepancy with recent renormalization group predictions are traced back to the effect of a dangerously irrelevant variable.
authors.affiliation: Theoretische Physik, Universität des Saarlandes, 66041 Saarbrücken, Germany.
authors.forename: André
authors.initials: A
authors.lastname: Winter
authors.forename: Heiko
authors.initials: H
authors.lastname: Rieger
authors.forename: Matthias
authors.initials: M
authors.lastname: Vojta
authors.forename: Ralf
authors.initials: R
authors.lastname: Bulla