Ground-state properties of sub-Ohmic spin-boson model with simultaneous diagonal and off-diagonal coupling

• Main Authors: Zhou, Nengji, Chen, Lipeng, Zhao, Yang, Mozyrsky, Dima, Chernyak, Vladimir
• Other Authors: School of Materials Science & Engineering
• Format: Article
• Language: English
• Published: 2014
• Subjects: DRNTU::Science::Physics::Atomic physics::Quantum theory
• Online Access: https://hdl.handle.net/10356/103101; http://hdl.handle.net/10220/24399
• Institution: Nanyang Technological University

By employing a variational approach, the density matrix renormalization group (DMRG), the exact diagonalization, and symmetry and mean-field analyses, the ground-state properties of the two-bath spin-boson model with simultaneous diagonal and off-diagonal coupling are systematically studied in the sub-Ohmic regime. A quantum phase transition from a doubly degenerate “localized phase” to the other doubly degenerate “delocalized phase” is uncovered. Via the multi-D1 Ansatz as the variational wave function, transition points are determined accurately, consistent with the results from DMRG and exact diagonalization. An effective spatial dimension deff=2.37(6) is then estimated, which is found to be compatible with the mean-field prediction. Furthermore, the quantum phase transition is inferred to be of first order for the baths described by a continuous spectral density function. In the single-mode case, however, the transition is softened.