# Observation of Floquet band topology change in driven ultracold Fermi gases

## TL;DR

This study directly measures Floquet band dispersions in a driven ultracold Fermi gas, demonstrating topological changes in Floquet bands through manipulation of Dirac points, advancing understanding of Floquet physics and topological quantum matter.

## Contribution

First direct measurement of Floquet band dispersions in a driven ultracold Fermi gas showing topological band changes via Dirac point manipulation.

## Key findings

- Dirac points can be shifted to different energy bands by modulating laser frequencies.
- Floquet band topology can be controlled experimentally in ultracold gases.
- The method provides insights into Floquet physics and topological matter engineering.

## Abstract

Periodic driving of a quantum system can significantly alter its energy bands and even change the band topology, opening a completely new avenue for engineering novel quantum matter. Although important progress has been made recently in measuring topological properties of Floquet bands in different systems, direct experimental measurement of Floquet band dispersions and their topology change is still demanding. Here we directly measure Floquet band dispersions in a periodically driven spin-orbit coupled ultracold Fermi gas. Using spin injection radio-frequency spectroscopy, we observe that the Dirac point originating from two dimensional spin-orbit coupling can be manipulated to emerge at the lowest or highest two dressed bands by fast modulating Raman laser frequencies, demonstrating topological change of Floquet bands. Our work will provide a powerful tool for understanding fundamental Floquet physics as well as engineering exotic topological quantum matter.