  Paradigmatic knotted solitons, Hopfions, that are characterized by
topological Hopf invariant, are widely investigated in the diverse areas
ranging from high energy physics, cosmology and astrophysics to biology,
magneto- and hydrodynamics and condensed matter physics. Yet, while holding
high promise for applications, they remain elusive and under-explored. Here we
demonstrate that Hopfions emerge as a basic configuration of polarization field
in confined ferroelectric nanoparticles. Our findings establish that Hopfions
govern a wealth of novel functionalities in the electromagnetic response of
composite nanomaterials opening route to unprecedented technological
applications.
