Evidence of Potts-Nematic Superfluidity in a Hexagonal $sp^2$ Optical Lattice

TL;DR

This paper reports the experimental observation of a novel three-state Potts-nematic superfluid phase in a hexagonal optical lattice loaded with cold atoms, revealing new symmetry-breaking phenomena in quantum gases.

Contribution

It introduces the first observation of Potts-nematic order in a cold atom system, demonstrating a three-fold symmetry breaking distinct from traditional Ising nematicity.

Findings

Observation of three-state Potts-nematic order in cold atoms.

Spontaneous breaking of three-fold lattice rotation symmetry.

Theoretical analysis explaining stabilization by inter-orbital mixing.

Abstract

As in between liquid and crystal phases lies a nematic liquid crystal, which breaks rotation with preservation of translation symmetry, there is a nematic superfluid phase bridging a superfluid and a supersolid. The nematic order also emerges in interacting electrons and has been found to largely intertwine with multi-orbital correlation in high-temperature superconductivity, where Ising nematicity arises from a four-fold rotation symmetry $C_4$ broken down to $C_2$. Here we report an observation of a three-state ($\mathbb{Z}_3$) quantum nematic order, dubbed "Potts-nematicity", in a system of cold atoms loaded in an excited band of a hexagonal optical lattice described by an $sp^2$-orbital hybridized model. This Potts-nematic quantum state spontaneously breaks a three-fold rotation symmetry of the lattice, qualitatively distinct from the Ising nematicity. Our field theory analysis shows that the Potts-nematic order is stabilized by intricate renormalization effects enabled by strong inter-orbital mixing present in the hexagonal lattice. This discovery paves a way to investigate quantum vestigial orders in multi-orbital atomic superfluids.