Emergent Orbital Skyrmion Lattice in a Triangular Atom Array

TL;DR

This paper demonstrates the spontaneous formation of a chiral Skyrmion lattice in a two-dimensional triangular optical lattice loaded with bosonic atoms in degenerate p-orbital bands, revealing novel orbital phenomena distinct from spin systems.

Contribution

It introduces the emergence of a Skyrmion lattice in a multi-orbital Bose-Hubbard model, highlighting the role of orbital symmetry and geometric frustration, confirmed by advanced numerical methods.

Findings

Skyrmion lattice forms in a large phase diagram regime.

Confirmed by bosonic dynamical mean-field theory and exact diagonalization.

Orbital Skyrmion state results from orbital symmetry and lattice frustration.

Abstract

Multi-orbital optical lattices have been attracting rapidly growing research interests 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 multi-orbital 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 in contrast to its spin analogue which largely requires spin-orbit couplings. 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 analogue.