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arXiv:2003.11829 · Physical Review A

Experimental realization of spin-tensor momentum coupling in ultracold Fermi gases

Donghao Li, Lianghui Huang, Peng Peng, Guoqi Bian, Pengjun Wang, Zengming Meng, Liangchao Chen, Jing Zhang

Published Jul 10, 2020• 25 citations
arXivHTMLPDF

Abstract

We experimentally realize spin-tensor momentum coupling (STMC) using three ground Zeeman states coupled by three Raman laser beams in an ultracold atomic system of $^{40}\mathrm{K}$ Fermi atoms. This type of STMC consists of two bright-state bands as a spin-orbit coupled spin-1/2 system and one dark-state middle band. Using radio-frequency spin-injection spectroscopy, we investigate the energy band of STMC. It is demonstrated that the middle state is a dark state in the STMC system. The experimental realization of STMC open the door for further exploring exotic quantum matter.

DOI
10.1103/physreva.102.013309

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We experimentally realize spin-tensor momentum coupling (STMC) using three ground Zeeman states coupled by three Raman laser beams in an ultracold atomic system of 40K^{40}\mathrm{K}40K Fermi atoms. This type of STMC consists of two bright-state bands as a spin-orbit coupled spin-1/2 system and one dark-state middle band. Using radio-frequency spin-injection spectroscopy, we investigate the energy band of STMC. It is demonstrated that the middle state is a dark state in the STMC system. The experimental realization of STMC open the door for further exploring exotic quantum matter.
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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.
We briefly review recent progress on ultracold atomic Fermi gases with different types of synthetic spin-orbit coupling, including the one-dimensional (1D) equal weight Rashba-Dresselhaus and two-dimensional (2D) Rasbha spin-orbit couplings. Theoretically, we show how the single-body, two-body and many-body properties of Fermi gases are dramatically changed by spin-orbit coupling. In particular, the interplay between spin-orbit coupling and interatomic interaction may lead to several long-sought exotic superfluid phases at low temperatures, such as anisotropic superfluid, topological superfluid and inhomogeneous superfluid. Experimentally, only the first type - equal weight combination of Rasbha and Dresselhaus spin-orbit couplings - has been realized very recently using a two-photon Raman process. We show how to characterize a normal spin-orbit coupled atomic Fermi gas in both non-interacting and strongly-interacting limits, using particularly momentum-resolved radio-frequency spectroscopy. The experimental demonstration of a strongly-interacting spin-orbit coupled Fermi gas opens a promising way to observe various exotic superfluid phases in the near future.
Abstract Spin-tensor-momentum coupling (STMC) induces dramatic change of the single-particle energy spectrum, resulting in rich and novel quantum ground state phases. Here, considering the atomic interactions, the STMC induced Z 2 symmetry breaking of the energy band, the tricritical point and the magnetic phase transitions in trapped STMC Bose–Einstein condensates are presented analytically and numerically. We demonstrate that the ground state momentum and spin tensor are coupled by STMC and the asymmetry of the energy band is persistent in STMC system, resulting in phase transition between magnetized and unmagnetized plane wave phases or between the two unmagnetized plane wave phases. The critical conditions for the phase transitions are obtained analytically, clarifying the physical mechanisms behind the phase transitions. Particularly, a tricritical point is predicted, where different types of energy band merge and the first-order phase transition and the second-order phase transition meet. Interestingly, it is shown that the ground state strongly depends on the external trapping potential, establishing a potential method for manipulating the phase transitions of the system. We provide a theoretical evidence for deep understanding and experimental manipulation of novel quantum phases in STMC systems.