Topological phase-transition characterization of the one-dimensional Ising chain in a longitudinal field
Yi Liao, Ping‐Xing Chen
Abstract
For the one-dimensional Ising chain with spin-$1/2$ and exchange couple $J$ in a steady transverse field(TF), an analytical theory has well been developed in terms of some topological order parameters such as Berry phase(BP). For a TF Ising chain, the nonzero BP which depends on the exchange couple and the field strength characterizes the corresponding symmetry breaking of parity and time reversal(PT). However, there apparently exists a topological phase transition for the one-dimensional infinite Ising chain in a longitudinal field(LF). If the LF is added at zero temperature, researchers believe that the LF also could influence the PT-symmetry and there exists the discontinuous BP. But the theoretic characterization has not been well founded. This paper tries to aim at this problem. With the Jordan-Wigner transformation, we give the four-fermion interaction form of the Hamiltonian in the one-dimensional Ising chain with a LF. And by the method of the mean-field theory, four-fermion interaction is well dealt with. We solve the ground state energy and the ground wave function in the momentum space. We discuss the nonzero BP and suggest that there exist topological transitions in the paramagnetic and diamagnetic cases.