Collective modes of ultracold fermionic alkaline-earth-metal gases with SU( N ) symmetry

Abstract

We calculate the collective modes of ultracold trapped alkaline-earth-metal fermionic atoms, which possess an $\mathrm{SU}(N$) symmetry of the nuclear spin degree of freedom and a controllable $N$, with $N$ as large as 10. We calculate the breathing and quadrupole modes of two-dimensional and three-dimensional harmonically trapped gases in the normal phase. We particularly concentrate on two-dimensional gases, where the shift is more accessible experimentally, and the physics has special features. We present results as a function of temperature, interaction strength, density, and $N$. We include calculations across the collisionless to hydrodynamic crossover. We assume the gas is interacting weakly, such that it can be described by a Boltzmann-Vlasov equation that includes both mean-field terms and the collision integral. We solve this with an approximate scaling ansatz, taking care in two dimensions to preserve the scaling symmetry of the system. We predict the collective-mode frequency shifts and damping, showing that these are measurable in experimentally relevant regimes. We expect these results to furnish powerful tools to characterize interactions and the state of alkaline-earth-metal gases, as well as to lay the foundation for future work, for example, on strongly interacting gases and $\mathrm{SU}(N)$ spin modes.