Observation of nodal-line semimetal with ultracold fermions in an optical lattice

TL;DR

This paper reports the first observation of a 3D nodal-line semimetal with ultracold fermions in an optical lattice, demonstrating a new method to detect 3D topological band structures using spin textures and quench dynamics.

Contribution

It introduces a novel experimental realization of a 3D topological semimetal with ultracold atoms and a technique to reconstruct 3D band topology from 2D measurements.

Findings

Observation of bulk line nodes in a 3D optical lattice

Detection of band inversion lines via topological quench dynamics

Reconstruction of 3D topological band structure from spin textures

Abstract

Observation of topological phases beyond two-dimension (2D) has been an open challenge for ultracold atoms. Here, we realize for the first time a 3D spin-orbit coupled nodal-line semimetal in an optical lattice and observe the bulk line nodes with ultracold fermions. The realized topological semimetal exhibits an emergent magnetic group symmetry. This allows to detect the nodal lines by effectively reconstructing the 3D topological band from a series of measurements of integrated spin textures, which precisely render spin textures on the parameter-tuned magnetic-group-symmetric planes. The detection technique can be generally applied to explore 3D topological states of similar symmetries. Furthermore, we observe the band inversion lines from topological quench dynamics, which are bulk counterparts of Fermi arc states and connect the Dirac points, reconfirming the realized topological band. Our results demonstrate the first approach to effectively observe 3D band topology, and open the way to probe exotic topological physics for ultracold atoms in high dimensions.