Chiral orbital order of interacting bosons without higher bands

TL;DR

This paper proposes a new method to realize chiral orbital order in bosonic gases using $$-flux plaquettes, leading to long-lived chiral superfluid and Mott insulator phases without relying on higher energy bands.

Contribution

It introduces a practical framework for inducing chiral orbital order in bosonic gases via $$-flux plaquettes, avoiding limitations of high-energy band methods.

Findings

Demonstrates emergence of chiral superfluid vortex lattice.

Identifies a phase transition to a chiral Mott insulator with strong interactions.

Shows long-lived gapped collective mode with local chiral currents.

Abstract

Ultracold atoms loaded into higher Bloch bands provide an elegant setting for realizing many-body quantum states that spontaneously break time-reversal symmetry through the formation of chiral orbital order. The applicability of this strategy remains nonetheless limited due to the finite lifetime of atoms in high-energy bands. Here we introduce an alternative framework, suitable for bosonic gases, which builds on assembling square plaquettes pierced by a $\pi$-flux (half a magnetic-flux quantum). This setting is shown to be formally equivalent to an interacting bosonic gas loaded into $p$ orbitals, and we explore the consequences of the resulting chiral orbital order, both for weak and strong onsite interactions. We demonstrate the emergence of a chiral superfluid vortex lattice, exhibiting a long-lived gapped collective mode that is characterized by local chiral currents. This chiral superfluid phase is shown to undergo a phase transition to a chiral Mott insulator for sufficiently strong interactions. Our work establishes coupled $\pi$-flux plaquettes as a practical route for the emergence of orbital order and chiral phases of matter.