  Understanding the properties of hypernuclei helps to constrain the
interaction between hyperon and nucleon, which is known to play an essential
role in determining the properties of neutron stars. Experimental measurements
have suggested that the hypertriton ($^3_\Lambda \text{H}$), the lightest
hypernucleus, exhibits a halo structure with a deuteron core encircled by a
$\Lambda$ hyperon at a distance of about 10 fm. This large $\Lambda-d$ distance
in $^3_\Lambda \text{H}$ wave function is found to cause a suppressed
$^3_\Lambda \text{H}$ yield and a softening of its transverse momentum ($p_T$)
spectrum in relativistic heavy-ion collisions. Within the coalescence model
based on nucleons and $\Lambda$ hyperons from a microscopic hybrid hydro model
with a hadronic afterburner for nuclear cluster production in Pb-Pb collisions
at $\sqrt{s_{NN}}$= 5.02 TeV, we show how this softening of the hypertriton
$p_T$ spectrum appears and leads to a smaller mean $p_T$ for $^3_\Lambda
\text{H}$ than for helium-3 ($^3$He). The latter is opposite to the predictions
from the blast-wave model which assumes that $^3_\Lambda \text{H}$ and $^3$He
are thermally produced at the kinetic freeze-out of heavy-ion collisions. The
discovered quantum mechanical softening of the (anti-)hypertriton spectrum can
be experimentally tested in relativistic heavy-ion collisions at different
collision energies and centralities and used to obtain valuable insights into
the mechanisms for light (hyper-)nuclei production in these collisions.
