Observation of a dynamical sliding phase superfluid with P-band bosons

TL;DR

This paper reports the experimental observation of a dynamical sliding phase superfluid in a nonequilibrium ultracold atomic system loaded into the P-band of an optical lattice, revealing a new type of exotic dynamical phase.

Contribution

It demonstrates the emergence of a sliding phase superfluid in a 3D ultracold gas via a novel nonequilibrium method, linking experimental results with a phenomenological energy transfer theory.

Findings

Robust superfluid coherence in pancake directions during intermediate times

No coherence observed in the lattice direction during the sliding phase

The sliding phase persists for tens of milliseconds

Abstract

Sliding phases have been long sought after in the context of coupled XY-models, as they are of relevance to various many-body systems such as layered superconductors, freestanding liquid-crystal films, and cationic lipid-DNA complexes. Here we report an observation of a dynamical sliding phase superfluid that emerges in a nonequilibrium setting from the quantum dynamics of a three-dimensional ultracold atomic gas loaded into the P-band of a one-dimensional optical lattice. A shortcut loading method is used to transfer atoms into the P-band at zero quasimomentum within a very short time duration. The system can be viewed as a series of "pancake"-shaped atomic samples. For this far-out-of-equilibrium system, we find an intermediate time window with a lifetime around tens of milliseconds, where the atomic ensemble exhibits robust superfluid phase coherence in the pancake directions, but no coherence in the lattice direction, which implies a dynamical sliding phase superfluid. The emergence of the sliding phase is attributed to a mechanism of cross-dimensional energy transfer in our proposed phenomenological theory, which is consistent with experimental measurements. This experiment potentially opens up a novel venue to search for exotic dynamical phases by creating high-band excitations in optical lattices.