Emergent orbital skyrmion lattice in a triangular atom array

Abstract

Multiorbital optical lattices have been attracting rapidly growing research interest in the last several years, providing fascinating opportunities for orbital-based quantum simulations. Here, we consider bosonic atoms loaded in the degenerate p-orbital bands of a two-dimensional triangular optical lattice. This system is described by a multiorbital Bose-Hubbard model. We find the confined atoms in this system develop spontaneous orbital polarization, which forms a chiral Skyrmion lattice pattern in a large regime of the phase diagram. This is an orbital version of the skyrmion, reminiscent of those in spin systems. The emergence of the Skyrmion lattice is confirmed in both bosonic dynamical mean-field theory (BDMFT) and exact diagonalization (ED) calculations. By analyzing the quantum-tunneling-induced orbital-exchange interaction in the strong interaction limit, we find the Skyrmion lattice state arises due to the interplay of p-orbital symmetry and the geometric frustration of the triangular lattice. We provide experimental consequences of the orbital Skyrmion state that can be readily tested in cold atom experiments. Our study implies orbital-based quantum simulations could bring exotic scenarios unexpected from their spin analog.