Dynamical Symmetry Enlargement versus Spin-Charge Decoupling in the One-Dimensional SU(4) Hubbard Model

We investigate dynamical symmetry enlargement in the half-filled SU(4) Hubbard chain using nonperturbative renormalization-group and quantum Monte Carlo techniques. A spectral gap is shown to open for arbitrary Coulombic repulsion $U$. At weak coupling, $U\lesssim 3t$, a SO(8) symmetry between charge and spin-orbital excitations is found to be dynamically enlarged at low energy whereas at strong coupling, $U\gtrsim 6t$, the charge degrees of freedom dynamically decouple. The crossover between these regimes is discussed.

Figure 1

One-particle gap ${\Delta }_1$, spin-orbital gap ${\Delta }_s$, and cooperon gap ${\Delta }_c$ as a function of $U/t$; inset: ${\Delta }_s$ gap as function of $U/t$.

Figure 2

Gap ratio ${\Delta }_1/{\Delta }_c$ as a function of $U/t$.