title: Gapless topological Fulde-Ferrell superfluidity in spin-orbit coupled Fermi gases.
abstract: Topological superfluids usually refer to a superfluid state which is gapped in the bulk but metallic at the boundary. Here we report that a gapless, topologically nontrivial superfluid with an inhomogeneous Fulde-Ferrell pairing order parameter can emerge in a two-dimensional spin-orbit coupled Fermi gas, in the presence of both in-plane and out-of-plane Zeeman fields. The Fulde-Ferrell pairing-induced by the spin-orbit coupling and in-plane Zeeman field-is responsible for this gapless feature. This exotic superfluid has a significant Berezinskii-Kosterlitz-Thouless transition temperature and has robust Majorana edge modes against disorder owing to its topological nature.
authors.affiliation: Centre for Quantum and Optical Science, Swinburne University of Technology, Melbourne 3122, Australia and State Key Laboratory of Low-dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, People's Republic of China.
authors.forename: Ye
authors.initials: Y
authors.lastname: Cao
authors.affiliation: State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
authors.forename: Shu-Hao
authors.initials: SH
authors.lastname: Zou
authors.affiliation: Centre for Quantum and Optical Science, Swinburne University of Technology, Melbourne 3122, Australia.
authors.forename: Xia-Ji
authors.initials: XJ
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
authors.forename: Su
authors.initials: S
authors.lastname: Yi
authors.affiliation: State Key Laboratory of Low-dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, People's Republic of China and Collaborative Innovation Center of Quantum Matter, Beijing 100084, People's Republic of China and Tsinghua National Laboratory for Information Science and Technology, Beijing 100084, People's Republic of China.
authors.forename: Gui-Lu
authors.initials: GL
authors.lastname: Long
authors.affiliation: Centre for Quantum and Optical Science, Swinburne University of Technology, Melbourne 3122, Australia.
authors.forename: Hui
authors.initials: H
authors.lastname: Hu