BCS-BEC Crossover and Topological Phase Transition in 3D Spin-Orbit Coupled Degenerate Fermi Gases

Understand

We investigate the BCS-BEC crossover in three dimensional degenerate Fermi gases in the presence of spin-orbit coupling (SOC) and Zeeman field.

• We show that the superfluid order parameter destroyed by a large Zeeman field can be restored by the SOC.
• With increasing strengths of the Zeeman field, there is a series of topological quantum phase transitions from a non-topological superfluid state with fully gapped fermionic spectrum to a topological superfluid state with four topologically protected Fermi points (i.e., nodes in the quasiparticle excitation gap) and then to a second topological superfluid state with only two topologically protected Fermi points.
• The quasiparticle excitations near the Fermi points realize the long-sought low-temperature analog of Weyl fermions of particle physics.