
Andreas Mielke
Institut for Theoretical Physics
RuprechtKarls University
Philosophenweg 19
D69120 Heidelberg
Germany
Tel.: ++49 6221 549431 (Secretary)
Fax: ++49 6221 549331
email:
mielke@tphys.uniheidelberg.de
Stefan Kehrein, Andreas Mielke, Peter Neu: Flow equations for the spinboson problem
Z. Phys. B99,
269280
(1996)
.
AbstractUsing continuous unitary transformations recently introduced by Wegner we obtain flow equations for the parameters of the spinboson Hamiltonian. Interactions not contained in the original Hamiltonian are generated by this unitary transformation. Within an approximation that neglects additional interactions quadratic in the bath operators, we can close the flow equations. Applying this formalism to the case of Ohmic dissipation at zero temperature, we calculate the renormalized tunneling frequency. We find a transition from an untrapped to a trapped state at the critical coupling constant $\alpha= 1$. We also obtain the static susceptibility via the equilibrium spin correlation function. Our results are both consistent with results known from the Kondo problem and those obtained from mode coupling theories. Using this formalism at finite temperature, we find a transition from coherent to incoherent tunneling at $T_2\approx T_1$, where $T_1$ is the corssover temperature of the dynamics from underdamped to overdamped motion known from the NIBA.
BibTeXentry
@article{Kehrein1996b,
author="Stefan Kehrein, Andreas Mielke, Peter Neu",
title="Flow equations for the spinboson problem",
journal="Z. Phys. B",
volume="99",
pages="269280",
year="1996"
}
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