Density Matrix Renormalization Group simulations of the SU(N) Fermi-Hubbard chain implementing the full SU(N) symmetry via Semi-Standard Young Tableaux and Unitary Group Subduction Coefficients

Abstract

We have developed an efficient method for performing density matrix renormalization group (DMRG) simulations of the SU(N) Fermi-Hubbard chain with open boundary conditions, fully leveraging the SU(N) symmetry of the problem. This method extends a previously developed approach for the SU(N) Heisenberg model and relies on the systematic use of the semi-standard Young tableaux (SSYT) basis in a DMRG algorithm `a la White. Specifically, the method aligns the site-by-site growth process of the infinite-size part of the DMRG, in its original formulation, with the site-by-site construction of the SSYT (or Gelfand-like) basis, based on the chain of unitary subgroups $U(1)\subset U(2) \subset U(3) \subset U(4)\cdots $. We give special emphasis to the calculation of the symmetry-resolved reduced matrix elements of the hopping terms between the left and the right block, which makes direct use of the basis of SSYT and of the Gelfand-Tsetlin coefficients, offering a computational advantage in scaling with N compared to alternative methods that rely on summing over Clebsch-Gordan coefficients. Focusing on the model with homogeneous hopping between nearest neighbors, we have calculated the ground state energy as a function of U, i.e the atom-atom interaction amplitude, up to N=6 for filling 1/N (one particle per site in average), and for one atom (resp. hole) away from filling 1/N, alllowing us to compute the charge gaps, and to estimate in the thermodynamical limit, the critical value $U_c$, separating the Mott insulator from the metallic phase. Central charges c are extracted from the entanglement entropy using the Calabrese-Cardy formula, and are consistent with the theoretical predictions: c=N-1, expected from the $SU(N)_1$ Wess-Zumino-Witten CFTs in the spin sector for the Mott phase, and c=N in the metallic phase, reflecting the presence of one additional (charge) gapless critical mode.