Spin-orbit-coupled atomic Fermi gases in two-dimensional optical lattices in the presence of a Zeeman field

Abstract

We investigate the single-particle and collective excitations of a Rashba spin-orbit coupled atomic Fermi gas with attractive interaction, loaded in a two dimensional (2D) square optical lattice, in the presence of an effective out-of-plane Zeeman field. Our numerical calculations show that the many body physics of the Bardeen-Cooper-Schrieffer (BCS) side is strongly modified compared to the Fermi gases in the free space. The physics behind this statement is in the fact that without a lattice structure, if the value of the Zeeman field does not exceed some threshold value, the minimum of the single-particle ground state energy is infinitely degenerate and occurs along a ring in $(k_x,k_y)$ space. This reduces the effective dimensionality; the single-particle density of states is a constant at low energies, and the molecular pairing is strongly enhanced. In contrast to the continuum, in the 2D lattice case there are only four degenerate minima, and because of that, the spin-orbit coupling (SOC) in optical lattices gives rise to unusual properties entirely different from the continuum. For example, in the continuum, the pairing gap as well as the condensate fraction are strongly enhanced by the SOC strength on the BCS side. In the presence of lattice geometry the gap and the condensate fraction increase as a function of the SOC strength only at the small fillings and weak attraction limit. Moreover, we found that the speed of sound also exhibits different behavior: in the 3D and 2D continuum, the slope of the Goldstone mode decreases as a function of the SOC strength, while in the lattice case the speed of sound increases monotonically with SOC strength.

14 pages, 11 figures

References in corpus (19)

• Non-Abelian Topological Order in S-Wave Superfluids of Ultracold Fermionic Atoms
• Degenerate Quantum Gases with Spin-Orbit Coupling
• A Bose-Einstein Condensate in a Uniform Light-induced Vector Potential
• Non-Abelian quantum order in spin-orbit-coupled semiconductors: The search for topological Majorana particles in solid state systems
• $p_x+i{p}_y$ superfluid from s-wave interactions of fermionic cold atoms
• Non-Abelian optical lattices: Anomalous quantum Hall effect and Dirac Fermions
• BCS-BEC crossover induced by a synthetic non-Abelian gauge field
• Unconventional superfluid in a two-dimensional Fermi gas with anisotropic spin-orbit coupling and Zeeman fields
• Ultracold atomic gas in non-Abelian "magnetic" fields: the quantum Hall effect supremacy
• Ultracold atomic gases in non-Abelian gauge potentials: The case of constant Wilson loop
• Bose-Einstein Condensates in Spin-Orbit Coupled Optical Lattices: Flat Bands and Superfluidity
• Fermi Gases with Synthetic Spin-Orbit Coupling
• Two-Dimensional Electron Gas with Cold Atoms in Non-Abelian Gauge Potentials
• Effects of spin-orbit coupling on the Berezinskii-Kosterlitz-Thouless transition and the vortex-antivortex structure in two-dimensional Fermi gases
• Topological superfluids on a lattice with non-Abelian gauge fields
• Superfluid Breakdown and Multiple Roton Gaps in Spin-Orbit Coupled Bose-Einstein Condensates on an Optical Lattice
• The Pairing of Spin-orbit Coupled Fermi Gas in Optical Lattice
• Topological superfluids on a square optical lattice with non-Abelian gauge fields: Effects of next-nearest-neighbor hopping in the BCS-BEC evolution
• Speed of sound of a spin balanced Fermi gas with s- and d-wave pairings across the BCS-BEC evolution

Cited by in corpus (4)

• Phase diagram, band structure and density of states in two-dimensional attractive Fermi-Hubbard model with Rashba spin-orbit coupling
• Bloch bound state of spin-orbit-coupled fermions in an optical lattice
• A universal pairing gap measurement proposal by dynamical excitations in 2D doped attractive Fermi-Hubbard model with spin-orbit coupling
• Critical temperature in the BCS-BEC crossover with spin-orbit coupling