Fermi-Liquid Behavior of the Normal Phase of a Strongly Interacting Gas of Cold Atoms

We measure the magnetic susceptibility of a Fermi gas with tunable interactions in the low-temperature limit and compare it to quantum Monte Carlo calculations. Experiment and theory are in excellent agreement and fully compatible with the Landau theory of Fermi liquids. We show that these measurements shed new light on the nature of the excitations of the normal phase of a strongly interacting Fermi gas.

Figure 1

Canonical equation of state of a two-component Fermi gas calculated using quantum Monte Carlo simulation, for $1/k_{F}a=-1.5$, $-1$, $-0.6$, $-0.2$, 0, 0.2, 0.4, 0.5 (from top to bottom). The solid lines are fits of the low-polarization data with Eq. (2). Inset: Extracted values of the susceptibility $\tilde{\chi }$ as a function of $1/k_{F}a$. The dashed red line is the result of a perturbation expansion valid up to order $(k_{F}a{)}^2$.

Figure 2

Thermodynamic function $h(b)$ measured at different magnetic fields $B_0=871$, 834, 822 G. The blue lines correspond to the superfluid equation of state $h_S(\delta )$ measured in [12]. The red line is a linear fit of the data in the normal phase, $b>b_c$. The dashed line indicates the superfluid/normal phase transition ($b=b_c$).

Figure 3

Fermi-liquid equation of state extrapolated to a spin-symmetric configuration $h_N(\delta )$. The black dots are the experimental data, and the red line is calculated from the Monte Carlo data. Inset: Grand-canonical susceptibility ${\tilde{\chi }}^{\mathrm{GC}}(\delta )$ of a Fermi gas in the BEC-BCS crossover.

Figure 4

Energy distribution data $\overline{A}(k,\omega )$ from [7] (red dots), compared with the prediction of Fermi-liquid theory (blue lines), for $k/k_F=0.3$, 0.6, 0.9, 1.2, 1.5.