CSU Physics Colloquium

Exotic paired states of Fermi gases in optical lattices
**Note the Start Time has been shifted this week to 4:30 pm**

Dr. Adrian Feiguin

University of Wyoming

Mon,  11/2

In recent years, amazing developments in atomic physics have enabled experimentalists to recreate model Hamiltonians in a lab, using lasers and neutral atoms, in setups that can be considered as analog quantum simulators. In particular, ultracold atoms in optical lattices can be used to study models of strongly correlated fermions in clean and controlled experimental conditions.

Recently, a great of attention is being devoted to the quest for unconventional superfluid states. One of these states is the one predicted by Fulde and Ferrell and Larkin and Ovchinnikov (FFLO state) over four decades ago. This state is theoretically possible in polarized Fermi mixtures, and has eluded condensed matter physicists until today.

Conventional superconductivity (BCS theory) consists of pairing between atoms with opposite spin, and equal but opposite momenta. In the FFLO state, pairing occurs across mismatched Fermi surfaces, so that the pairs have finite center of mass momentum. In this talk I will make a case for realizing it in low-dimensional traps, and I will illustrate it with exact results in one-dimensional chains and quasi-one-dimensional ladders.

The power to control the experimental conditions also allows for engineering spin-dependent optical lattices. These, in turn, can be used to create a Fermi mixture that is unpolarized, but still, with mismatched Fermi surfaces. I will propose an experiment in which fermions with opposite spin have elongated Fermi surfaces that are rotated 90 degrees with respect to one another. With this simple setup, we find the existence of unusual paired states similar, in some cases, to those found in polarized mixtures. We also propose the existence of an exotic “Cooper-pair Bose-Metal”, which has gapless “Cooper pair” excitations residing on a “Bose-surface” in momentum space.