Field-induced quantum phase transitions in S = 1/2 J₁-J₂ Heisenberg model on square lattice

We study the magnetic field dependence of the ground state of the S = 1/2 J₁-J₂ Heisenberg model on the square lattice by the density matrix renormalization group (DMRG) method. With the use of the sine-square deformation, we obtain eight different ground states including plaquette valence-bond crystal with a finite spin gap, transverse Néel, transverse stripe, 1/2 magnetization plateau with up-up-up-down (uuud), and three new states we named the Y-like, V-like, and Ψ states around J₂/J₁ = 0.55-0.6. The phase transitions from the transverse Néel (at J₂/J₁ = 0.55) and stripe (at J₂/J₁ = 0.6) states to the uuud and Y-like states, respectively, are discontinuous, as in the case of a spin flop.