Fermi Gases in Bichromatic Superlattices

Fermi Gases in Bichromatic Superlattices

Designer materials made of ultra-cold atoms and light provide new paradigms for emulating exotic layered systems. Bichromatic superlattices, comprising standing waves at two optical wavelengths, enable control and study of both dimensionality and dispersion in layered, strongly correlated Fermi gases, offering new opportunities in the search high-temperature superconductors and superfluids.

Most layered materials are quasi-two-dimensional, neither two-dimensional, like a sheet, nor three-dimensional, like a gas, but somewhere in between. In quasi-2D layers with an unequal number of spin-up and spin-down electrons, particularly strong attraction between pairs of electrons with opposite spins is predicted to achieve the highest possible superconducting transition temperatures, needed for practical super-efficient power transmission. To understand these materials, we emulate them with a layered, ultra-cold Fermi gas of atoms, where precise control of the attraction, spin-composition, dimensionality and dispersion provides new tests of theory.

The proposed program examines the properties of mesoscopic Fermi gas layers, containing several hundred atoms each, which are created by combining the tunable periodic potential of a bichromatic superlattice along one axis, with the smooth potential of a CO2 laser trap that provides tunable confinement along the orthogonal (transverse) axes. The data obtained using this non-perturbative many-body system will enable precise feedback between theory, computation and experiment, to test state-of-the-art calculational methods, which are an important focus of the DOE theory program.

Experiments employing this new trapping system will be used to address two important scientific goals: 1) Elucidation of the effects of dimensionality and confining potential shape on the enhancement of high-temperature superfluidity in a layered, strongly correlated Fermi gases; 2) Control of dispersion and the study of tunable Dirac points in one dimension, where the cloud behaves as a relativistic gas.