Second-order Peierls transition in the spin-orbital Kumar-Heisenberg model

摘要: We add a Heisenberg interaction term $\ensuremath{\propto}\ensuremath{\lambda}$ in the one-dimensional $\text{SU}(2)\ensuremath{\bigotimes}\mathit{\text{XY}}$ spin-orbital model introduced by Kumar. At $\ensuremath{\lambda}=0$ spin and orbital degrees of freedom can be separated unitary transformation leading to an exact solution model. show that finite $\ensuremath{\lambda}g0$ leads spontaneous dimerization system which thermodynamic limit becomes smooth phase transition at $\ensuremath{\lambda}\ensuremath{\rightarrow}0$, whereas it remains discontinuous within first-order perturbation approach. present behavior entanglement entropy, energy gap, order parameter $\ensuremath{\lambda}\ensuremath{\rightarrow}0$ confirming critical behavior. Finally, we evidence another limit, $\ensuremath{\lambda}\ensuremath{\rightarrow}\ensuremath{\infty}$, give qualitative analytical explanation observed dimerized states both small large $\ensuremath{\lambda}$.