Two-dimensional FFLO vortex lattices and vortex liquids

R.N. Ignatiev, Edouard B Sonin

Predrag Nikolić

By analyzing vortex lattices, re-entrant Cooper pairing, and Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states in a single theoretical framework, we explore how vortices and spin textures join to protect superconductivity against large magnetic fields. We use a rapidly rotating ultracold gas of fermionic atoms near unitarity as a model system amenable to experimental exploration and discover a hierarchy of spin-polarized and FFLO phases in which a metal or a band insulator of unpaired particles coexists with a spatially modulated superfluid hosting a vortex lattice. Quantum fluctuations can transform these phases into strongly correlated ``vortex-liquid'' metals and insulators, respectively. We argue that vortex lattices significantly enhance the stability of FFLO states and discuss prospects for observing these states in cold-atom experiments.

Bose-Einstein Condensates

Calvin Bales, Raju Prasad Ghimire, V. F. Mitrović +3 more

D. F. Agterberg, Michael Geracie, Hirokazu Tsunetsugu

We consider defect-mediated melting of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) and pair density wave (PDW) phases in two dimensions. Examining mean-field ground states in which the spatial oscillations of the FFLO/PDW superfluid order parameter exhibit hexagonal lattice symmetry, we find that thermal melting leads to a variety of novel phases. We find that a spatially homogeneous charge 6 superfluid can arise from melting a hexagonal vortex-antivortex lattice FFLO/PDW phase. The charge 6 superfluid has an order parameter corresponding to a bound state of six fermions. We further find that a hexagonal vortex-free FFLO/PDW phase can melt to yield a conventional (charge 2) homogeneous superfluid. A key role is played by topological defects that combine fractional vortices of the superfluid order and fractional dislocations of the lattice order.

Thierry Giamarchi, Pierre Le Doussal