Search for the FFLO phase in the 1D-3D Crossover of a Spin-Imbalanced Fermi Gas

The Fulde-Ferrell Larkin-Ovchinnikov (FFLO) type superconductor is an exotic form of matter known as a supersolid because it simultaneously supports superfluid and magnetic order. In both condensed matter and ultracold atomic gases, this phase has yet to be conclusively observed despite long interest in both theory and experiment. In one-dimension (1D), unlike expectations for higher dimensions, the FFLO phase is found in a large region of the phase diagram¹. The effect of quantum and thermal fluctuations, however, are expected to be reduced in higher dimensions. These considerations motivated the proposal to search for FFLO near the 1D-3D dimensional crossover², which we have identified and characterized³. We confine a spin-imbalanced Fermi gas of 6Li to an array of 1D tubes using a 2D optical lattice. We bring the system into the dimensional crossover by increasing the inter-tube tunneling rate and using a Feshbach resonance to tune interactions. We present our progress towards direct observation of the domain walls containing the excess unpaired fermions. The periodicity of these domain walls, which depends on the magnitude of the polarization, is a definitive signature of the FFLO phase.

¹ Y.-A. Liao et al. Nature. 467, 567-569 (2010) 

² M. M. Parish et al. Phys. Rev. Lett. 99, 250403 (2007)

³ M. C. Revelle et al. Phys. Rev. Lett. 117, 235301 (2016)