Fulde-Ferrell Superfluids in Degenerate Fermi Gases with Synthetic Gauge Fields

Zhen Zheng, Z D Wang

Abstract We here present an experimentally feasible proposal for manipulating Cooper pairs in degenerate Fermi gases trapped by an optical lattice. Upon introducing an in situ periodically driven field, the system may be described by an effective time-independent Hamiltonian, in which the Cooper pairs, generated by the bound molecule state in Feshbach resonance, host a nonzero center-of-mass momentum. The system thus processes a crossover from a Bardeen–Cooper–Schrieffer superfluid phase to a Fulde–Ferrell (FF) one. Furthermore, the magnitude and direction of the Cooper pairs in the synthetic FF superfluids are both directly controllable via the periodically driven field. Our proposal offers a reliable and feasible scenario for manipulating the Cooper pairs in cold atoms, serving as a tunable as well as powerful platform for quantum-emulating and exploring the FF superfluid phase.

S. J. J. M. F. Kokkelmans, Murray Holland, R. Walser +1 more

Georgy V. Shlyapnikov

Hui Hu, Xia-Ji Liu

We theoretically investigate the inhomogeneous Fulde–Ferrell (FF) superfluidity in a three-dimensional atomic Fermi gas with Rashba spin–orbit coupling near a broad Feshbach resonance. We show that within mean-field theory the FF superfluid state is always more favorable than the standard Bardeen–Cooper–Schrieffer superfluid state when an in-plane Zeeman field is applied. We present a qualitative finite-temperature phase diagram near resonance and argue that the predicted FF superfluid is observable with experimentally attainable temperatures (i.e. T ∼ 0.2 T F , where T F is the characteristic Fermi degenerate temperature).

Zhen Zheng, Ming Gong, Yichao Zhang +3 more

We show that the combination of spin-orbit coupling and in-plane Zeeman field in a two-dimensional degenerate Fermi gas can lead to a larger parameter region for Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases than that using spin-imbalanced Fermi gases. The resulting FFLO superfluids are also more stable due to the enhanced energy difference between FFLO and conventional Bardeen-Cooper-Schrieffer (BCS) excited states. We clarify the crucial role of the symmetry of Fermi surface on the formation of finite momentum pairing. The phase diagram for FFLO superfluids is obtained in the BCS-BEC crossover region and possible experimental observations of FFLO phases are discussed.

Wolfgang Ketterle, Yong-il Shin, André Schirotzek +1 more