(Received August 21, 1989)
We study the ground state energy and the excitation spectra of a spin-boson system in the case of white bath limit as well as in the case of white bath on the basis of a recent theory proposed by the author. We confirm the previous numerical results in the case of non-white bath. Our analytical findings are as follows. (1) The ground state in the case of white bath is the tunneling state for s>1 and the localized state for 1 ≥s>0, where s is the power of the frequency dependence of the spectral density of interaction. (2) The ground state in the white bath limit differs from that in the white bath for s=1, that is, the former does not change into the latter continuously, while the latter is the limit of the former for 1>s>0. (3) The low-lying excitations form gapless continuum above the ground state energy. There appears another continuum shifted upward by the tunneling gap when the tunneling ground state exists.
URL : http://ptp.ipap.jp/link?PTP/83/29/
DOI : 10.1143/PTP.83.29