  Yang monopole as a zero-dimensional topological defect has been well
established in multiple fields in physics. However, it remains an intriguing
question to understand interaction effects on Yang monopoles. Here, we show
that collective motions of many interacting bosons give rise to exotic
topological defects that are distinct from Yang monopoles seen by a single
particle. Whereas interactions may distribute Yang monopoles in the parameter
space or glue them to a single giant one of multiple charges, three-dimensional
topological defects also arise from continuous manifolds of degenerate
many-body eigenstates. Their projections in lower dimensions lead to knotted
nodal lines and nodal rings. Our results suggest that ultracold bosonic atoms
can be used to create emergent topological defects and directly measure
topological invariant that are not easy to access in solids.
