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TT: Tiefe Temperaturen

TT 35: Correlated Electrons - Quantum Critical Phenomena

TT 35.6: Talk

Wednesday, March 9, 2005, 12:30–12:45, TU H104

NRG Study of the Quantum Critical Properties of the Sub-Ohmic Spin-Boson Model — •Ninghua Tong¹, Matthias Vojta¹, and Ralf Bulla² — ¹Institute for Theory of Condensed Matter, University of Karlsruhe — ²Theoretical Physics III, Institute for Physics, University of Augsburg

Using the bosonic numerical renormalization group technique, we study the quantum critical properties of the sub-Ohmic spin-boson model. This model describes a two-level system imbedded in a bosonic bath with power-law spectrum density J(ω) ∼ ω^s. In the sub-Ohmic regime 0<s<1, there exists a line of quantum critical points separating localized and delocalized phases. The critical exponents are calculated and the hyperscaling relations are found to be fulfilled in the range 0<s<1. In small s limit, these results agree well with the perturbative RG calculation, but contradict the existing results for the corresponding long-range Ising model. We conclude that the naive quantum-classical mapping fails for the spin-boson model in the regime 0<s<1/2.