Is there a pairing pseudogap above $T_{\mathrm{c}}$ in the unitary gas?
In plain words
Atoms may form short-lived pairs above the temperature where they become superfluid, opening a partial energy gap. Experiments disagree on whether this gap exists.
Precise statement
Homogeneous unitary gas for $T_{c} < T < 1.5 T_{c}$. Measure the single-particle spectral function $A(k, \omega)$ and determine whether spectral weight at $k = k_{F}$ and $\omega = 0$ is suppressed, the gap scale $\Delta_{\mathrm{pg}}$, and the temperature $T*$ where it closes. Answer: $T*/T_{c}$ and $\Delta_{\mathrm{pg}}/E_{F}$ with errors, or an upper bound excluding a gap.
What would settle it
Momentum-resolved spectroscopy of a uniform gas with final-state effects removed, reproduced by two independent groups.
Status in the literature
Unverified note
A 2024 microwave-spectroscopy experiment reported a pseudogap (Li et al., Nature 626, 288), while earlier rf studies of uniform gases were interpreted without one.