# Collective excitations in two-dimensional SU($N$) Fermi gases with tunable spin

## TL;DR

This study measures and analyzes collective excitations in a 2D SU(N) Fermi gas of ytterbium, revealing how spin components influence mode frequencies and damping, and exploring the dimensional crossover from 2D to 3D.

## Contribution

It provides the first experimental observation of how collective mode frequencies in a 2D SU(N) Fermi gas depend on the number of spin components, confirming theoretical predictions.

## Key findings

- Quadrupole mode frequency decreases with increasing N.
- Breathing mode frequency remains twice the dipole frequency regardless of N.
- Enhanced inter-particle collisions observed for larger spin N.

## Abstract

We measure collective excitations of a harmonically trapped two-dimensional (2D) SU($N$) Fermi gas of $^{173}$Yb confined to a stack of layers formed by a one-dimensional optical lattice. Quadrupole and breathing modes are excited and monitored in the collisionless regime $\lvert\ln(k_F a_{2D})\rvert\gg 1$ with tunable spin. We observe that the quadrupole mode frequency decreases with increasing number of spin components due to the amplification of the interaction effect by $N$ in agreement with a theoretical prediction based on 2D kinetic equations. The breathing mode frequency, however, is measured to be twice the dipole oscillation frequency regardless of $N$. We also follow the evolution of collective excitations in the dimensional crossover from two to three dimensions and characterize the damping rate of quadrupole and breathing modes for tunable SU($N$) fermions, both of which reveal the enhanced inter-particle collisions for larger spin. Our result paves the way to investigate the collective property of 2D SU($N$) Fermi liquid with enlarged spin.