Parity Symmetry and Parity Breaking in the Super-Ohmic Spin-Boson Model

The parity symmetry and parity breaking in the super-Ohmic spin-boson model (SBM) is studied by using the coherent-state approach. We show that the parity symmetry is broken as well as the scaling behavior of the ground state by introducing a bias, and then it can be restored by involving an additional spin into the SBM to couple with the original spin by an Ising interaction. The rule can be found that the parity symmetry is broken by introducing a bias and then restored by adding new degrees of freedom.