  We report the formation of a pinned vortex liquid spanning a very large
region of the magnetic field-temperature parameter space in a 5 nm thick
amorphous superconducting Re_xZr (x~6) (a-ReZr) thin film, using a combination
of low-temperature scanning tunnelling spectroscopic (STS) imaging and
magnetotransport measurements. The nature of the vortex liquid differs
significantly from a regular liquid. Analysing series of STS images captured as
a function of time, we observe that the interplay of pinning and intervortex
interactions produces a very inhomogeneous state, where some vortices remain
static, whereas others move forming a percolating network along which vortices
are mobile. With increase in temperature or magnetic field this network becomes
denser eventually encompassing all vortices. Our results provide key insight on
the nature of a pinned vortex liquid and some of the peculiarities in the
transport properties of ultrathin superconducting films.
