  The epochs of cosmic dawn and reionisation present promising avenues for
understanding the role of dark matter (DM) in our cosmos. The first galaxies
that populated the Universe during these eras resided in DM halos that were
much less massive than their counterparts today. Consequently, observations of
such galaxies can provide us with a handle on the clustering of DM in an
otherwise currently inaccessible regime. In this work, we use high-redshift UV
galaxy luminosity-function (UV LF) data from the Hubble Space Telescope to
study the clustering properties of DM at small scales. In particular, we
present new measurements of the matter power spectrum at wavenumbers
$0.5\,\mathrm{Mpc}^{-1} < k < 10\,\mathrm{Mpc}^{-1}$ to roughly 30% precision,
obtained after marginalising over the unknown astrophysics. These new data
points cover the uncharted redshift range $4\leq z\leq 10$ and encompass scales
beyond those probed by Cosmic-Microwave-Background and large-scale-structure
observations. This work establishes the UV LF as a powerful tool to probe the
nature of DM in a different regime than other cosmological and astrophysical
data sets.
