Atom-resolved microscopy of exotic superfluids in spin-imbalanced Fermi gases

Princeton University, Princeton NJ

Investigators

Abstract

Non-technical: Superconductors, materials that have electrical currents that flow without losses, have important applications in building powerful electromagnets, sensitive sensors of magnetic fields and magnetic levitation devices. Understanding the behavior of superconductors in magnetic fields is crucial to building better superconducting devices. While large magnetic fields usually suppress superconductivity, they have also been predicted to lead to exotic superconducting phases of matter under the proper conditions. One such phase was proposed over fifty years ago, but has never been directly observed in any material. This research effort aims to discover this phase of matter in a gas of atoms cooled to very low temperatures. On the educational side, the project trains undergraduates, graduate students and a post-doctoral researcher in the techniques of ultracold gases. To complement the experimental effort, the principal investigator is developing and teaching a graduate course in ultracold atom physics, focusing on experimental techniques and potential applications. The course serves to train graduate students from the PI's lab in teaching through guest lecture opportunities. Technical: The competition between superconductivity and magnetism can give rise to exotic phases of quantum matter. Over fifty years ago, Fulde, Ferrell, Larkin and Ovchinnikov (FFLO) predicted a quantum phase where the Cooper pairs of a superconductor in a magnetic field condense at non-zero momentum. There has been indirect evidence for the existence of this phase in layered organic superconductors, heavy fermion materials and ultracold atomic gases, but a direct detection of its defining signatures has been elusive. The goal of this project is the direct detection of the FFLO phase in a superfluid atomic Fermi gas with spin imbalance. The research team uses atom-resolved in-situ imaging of the gas to search for its smoking gun signature: a spatial oscillation of the magnetization and superfluid gap that depends on the polarization of the gas. The search for this phase is conducted in a lower-dimensional lattice system where Fermi surface nesting effects are predicted to enhance the region of the phase diagram occupied by the FFLO phase. The team seeks to understand the low-temperature phase diagram of spin-imbalanced two-dimensional Fermi gases, use quantum gas microscopy to image imprinted solitonic lattices through the sharp variation of their magnetization and local density of states and apply these imaging techniques to search for FFLO in a thermal equilibrium state.