Loop-current orderings in SU($N$) two-leg fermionic ladder through duality symmetries
We investigate the formation of loop-current ordered phases in half-filled SU($N$) two-leg fermionic ladders. Using a low-energy approach, we uncover the existence of non-perturbative duality symmetries relating four competing orders. Two of these orders correspond to loop-current ordered phases that spontaneously break the time-reversal symmetry and describe charge currents circulating in a staggered pattern either around the plaquettes or along the diagonals of the ladder. These unconventional phases are shown to be dual to conventional (charge and bond) density-wave phases through an exact density-current duality symmetry existing on the lattice. From a perturbative renormalization group approach, we find that these phases for $N>2$ are stabilized in a half-filled SU($N$) two-leg Hubbard ladder with an additional SU($N$) Hund's interaction. The effect of a small doping on these phases is also discussed.