  The means by which the turbulent cascade of energy is dissipated in the solar
wind, and in other astrophysical systems, is a major open question. It has
recently been proposed that a barrier to the transfer of energy can develop at
small scales, which can enable heating through ion-cyclotron resonance, under
conditions applicable to regions of the solar wind. Such a scenario
fundamentally diverges from the standard picture of turbulence, where the
energy cascade proceeds unimpeded until it is dissipated. Here, using data from
NASA's Parker Solar Probe, we find that the shape of the magnetic energy
spectrum around the ion gyroradius varies with solar wind parameters in a
manner consistent with the presence of such a barrier. This allows us to
identify critical values of some of the parameters necessary for the barrier to
form; we show that the barrier appears fully developed for ion plasma beta of
below $\simeq0.5$ and becomes increasingly prominent with imbalance for
normalised cross helicity values greater than $\simeq0.4$. As these conditions
are frequently met in the solar wind, particularly close to the Sun, our
results suggest that the barrier is likely playing a significant role in
turbulent dissipation in the solar wind and so is an important mechanism in
explaining its heating and acceleration.
