Ultracold Gases of Ytterbium: Ferromagnetism and Mott States in an SU(6) Fermi System

TL;DR

This paper explores the properties of ultracold ytterbium gases with SU(6) symmetry, analyzing ferromagnetism and Mott states, and predicts phase transitions and stability conditions using theoretical models.

Contribution

It provides a theoretical analysis of SU(6) symmetry in ultracold ytterbium gases, including ferromagnetic transitions and Mott state coexistence in optical lattices.

Findings

Ferromagnetic transition is first order within mean-field theory.

SU(6) Mott states coexist with other phases at current experimental temperatures.

Stability of ferromagnetic states can be enhanced by optical methods or lattice tuning.

Abstract

It is argued that ultracold quantum degenerate gas of ytterbium $^{173}$Yb atoms having nuclear spin $I = 5/2$ exhibits an enlarged SU$(6)$ symmetry. Within the Landau Fermi liquid theory, stability criteria against Fermi liquid (Pomeranchuk) instabilities in the spin channel are considered. Focusing on the SU$(n > 2)$ generalizations of ferromagnetism, it is shown within mean-field theory that the transition from the paramagnet to the itinerant ferromagnet is generically first order. On symmetry grounds, general SU$(n)$ itinerant ferromagnetic ground states and their topological excitations are also discussed. These SU$(n > 2)$ ferromagnets can become stable by increasing the scattering length using optical methods or in an optical lattice. However, in an optical lattice at current experimental temperatures, Mott states with different filling are expected to coexist in the same trap, as obtained from a calculation based on the SU$(6)$ Hubbard model.