  Two-dimensional (2D) van der Waals (vdW) materials show a range of profound
physical properties that can be tailored through their incorporation in
heterostructures and manipulated with external forces. The recent discovery of
long-range ferromagnetic order down to atomic layers provides an additional
degree of freedom in engineering 2D materials and their heterostructure devices
for spintronics, valleytronics and magnetic tunnel junction switches. Here,
using direct imaging by cryo-Lorentz transmission electron microscopy we show
that topologically nontrivial magnetic-spin states, skyrmionic bubbles, can be
realized in exfoliated insulating 2D vdW Cr2Ge2Te6. Due to the competition
between dipolar interactions and uniaxial magnetic anisotropy,
hexagonally-packed nanoscale bubble lattices emerge by field cooling with
magnetic field applied along the out-of-plane direction. Despite a range of
topological spin textures in stripe domains arising due to pair formation and
annihilation of Bloch lines, bubble lattices with single chirality are
prevalent. Our observation of topologically-nontrivial homochiral skyrmionic
bubbles in exfoliated vdW materials provides a new avenue for novel quantum
states in atomically-thin insulators for magneto-electronic and quantum
devices.
