Symmetries in the Hubbard model with n-fold orbital degeneracy

Abstract

The present paper studies the symmeries of the Hubbard model of electrons with generally $n$-fold orbital degeneracy. It's shown SU_d(2n) and SU_c(2n) symmetries hold respectively for the model with completely repulsive or attractive on-site interaction and that with partly attractive interactions. An extended Lieb-Mattis transformation is given to map these two symmetries into each other. The sub-symmetry SU_d^{(e)}(n)\otimes SU_d^{(o)}(n) is found to be shared by the two models with arbitrary chemical potential \mu. By assuming at most two electrons on each site it's found that $SU_d(2n)$ and $SU_c(2n)$ both exist in each kind of the two models and consequently lead to a larger symmetry SU_d(2n)\times SU_c(2n). Another underlying symmetry SU_c^{(e)}(2)_{{\cal P}}\times ...\times SU_c^{(e)}(2)_{{\cal P}} \otimes \bigl(SU_c^{(o)}(2)_{{\cal P}}\times ...\times SU_c^{(o)}(2)_{{\cal P}}\bigr) is also revealed for the unified $U$ model under the excluding. The symmetry is valid for the partially attractive model with chemical potential $\mu =-U.$