Spin-orbital dynamics in a system of polar molecules

TL;DR

This paper demonstrates that dipole-dipole interactions in ultracold polar molecule gases can induce an effective spin-orbit coupling, leading to chiral excitations called chirons with potential observable effects in current experiments.

Contribution

It introduces a novel method to generate spin-orbit coupling using dipole interactions in ultracold molecules, independent of quantum statistics and energy ratios.

Findings

Chirons exhibit a non-trivial Berry phase of 2π.

Chirons influence spin density dynamics, currents, and coherences.

The phenomena are observable in existing ultracold molecule experiments.

Abstract

Spin-orbit coupling (SOC) in solids normally originates from the electron motion in the electric field of the crystal. It is key to understanding a variety of spin-transport and topological phenomena, such as Majorana fermions and recently discovered topological insulators. Implementing and controlling spin-orbit coupling is thus highly desirable and could open untapped opportunities for the exploration of unique quantum physics. Here, we show that dipole-dipole interactions can produce an effective SOC in two-dimensional ultracold polar molecule gases. This SOC generates chiral excitations with a non-trivial Berry phase $2\pi$. These excitations, which we call \emph{chirons}, resemble low-energy quasiparticles in bilayer graphene and emerge regardless of the quantum statistics and for arbitrary ratios of kinetic to interaction energies. Chirons manifest themselves in the dynamics of the spin density profile, spin currents, and spin coherences, even for molecules pinned in a deep optical lattice and should be observable in current experiments.