Ground-State Behavior of the Quantum Compass Model in an External Field

Ground-state (GS) properties of the two-dimensional (2D) quantum compass model in an external field on a square 5×5 lattice are investigated by using the exact diagonalization (ED) method. We obtain the GS energy and evaluate quantities such as its correlation functions, nearest-neighbor entanglement and local order parameter. As the external field is presented, the first-order quantum phase point is absent and the system exhibits the behaviors of the second-order phase transition.