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arXiv:2112.05898 · Physical Review A

Itinerant ferromagnetism of a dipolar Fermi gas with Raman-induced spin-orbit coupling

Xue-Jing Feng, Xing-Dong Zhao, Lu Qin, Yingying Zhang, Zunlue Zhu, Hong-juan Tian, Lin Zhuang, Wu‐Ming Liu

Published May 31, 2022• 2 citations
arXivHTMLPDF

Abstract

We elucidate the itinerant ferromagnetism of a dipolar Fermi gas with a Raman-induced spin-orbit coupling by investigating the exotic phase diagrams. It is revealed that the dipolar interaction along with spin-orbit coupling can corroborate the formation of ferromagnetism and that the Raman coupling adversely eliminates the tendency to this ferromagnetism transition, which greatly transcends the general understanding of this subject with contact interaction only. We explore the ground states through the density and spin-flip distribution in momentum space. We calculate the transition temperatures well within the reach of an experimental system when altering the dipolar and spin-orbit-coupling strength, which paves a way to the further experimental realization.

DOI
10.1103/physreva.105.053312

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We elucidate the itinerant ferromagnetism of a dipolar Fermi gas with a Raman-induced spin-orbit coupling by investigating the exotic phase diagrams. It is revealed that the dipolar interaction along with spin-orbit coupling can corroborate the formation of ferromagnetism and that the Raman coupling adversely eliminates the tendency to this ferromagnetism transition, which greatly transcends the general understanding of this subject with contact interaction only. We explore the ground states through the density and spin-flip distribution in momentum space. We calculate the transition temperatures well within the reach of an experimental system when altering the dipolar and spin-orbit-coupling strength, which paves a way to the further experimental realization.
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We study the ferromagnetic transition of a two-component homogeneous dipolar Fermi gas with 1D spin–orbit coupling (SOC) at finite temperature. The ferromagnetic transition temperature is obtained as functions of dipolar constant λ d, spin–orbit coupling constant λ SOC and contact interaction constant λ s. It increases monotonically with these three parameters. In the ferromagnetic phase, the Fermi surfaces of different components can be deformed differently. The phase diagrams at finite temperature are obtained.
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We consider a mixture of spin-1/2 bosons and fermions, where only the bosons are subjected to the spin-orbit coupling induced by Raman beams. The fermions, although not directly coupled to the Raman lasers, acquire an effective spin-orbit coupling through the spin-exchange interaction between the two species. Our calculation shows that this is a promising way of obtaining spin-orbit coupled Fermi gas without Raman-induced heating, where the long-sought topological Fermi superfluids and topological bands can be realized. Conversely, we find that the presence of fermions not only provides a new way to create the supersolid stripe phase of the bosons, but more strikingly it can also greatly increase the spatial period of the bosonic density stripes, and hence makes this phase directly observable in the experiment. This system provides a new and practical platform to explore the physics of spin-orbit coupling, which possesses a dynamic nature through the interaction between the two species.
We review our recent experimental realization and investigation of a spin-orbit (SO) coupled Bose-Einstein condensate (BEC) and quantum degenerate Fermi gas. By using two counter-propagating Raman lasers and controlling the different frequency of two Raman lasers to engineer the atom-light interaction, we first study the SO coupling in BEC. Then we study SO coupling in Fermi gas. We observe the spin dephasing in spin dynamics and momentum distribution asymmetry of the equilibrium state as hallmarks of SO coupling in a Fermi gas. To clearly reveal the property of SO coupling Fermi gas, we also study the momentum-resolved radio-frequency spectroscopy which characterizes the energy-momentum dispersion and spin composition of the quantum states. We observe the change of fermion surfaces in different helicity branches with different atomic density, which indicates that a Lifshitz transition of the Fermi surface topology change can be found by further cooling the system. At last, we study the momentum-resolved Raman spectroscopy of an ultracold Fermi gas.