Comparison of quasiparticle energy dispersions and shadow peaks of doped two-leg ladder systems between various models including anSO(5)symmetry model

Abstract

Considering various models including an $\mathrm{SO}(5)$ symmetry model, mean-field and exact diagonalization studies on the quasiparticle excitation of two-leg ladder systems are reported. It is shown that the energy gap in the quasiparticle excitation is caused by the formation of rung singlet states. We find that shadow peaks can occur above the Fermi surface with antiferromagnetic electron correlations involving only rungs in the spin ladder.