  Local-probe imaging of the ferroelectric domain structure and auxiliary bulk
pyroelectric measurements were conducted at low temperatures with the aim to
clarify the essential aspects of the orbitally driven phase transition in
GaMo4S8, a lacunar spinel crystal that can be viewed as a spin-hole analogue of
its GaV4S8 counterpart. We employed multiple scanning probe techniques combined
with symmetry and mechanical compatibility analysis to uncover the hierarchical
domain structures, developing on the 10-100 nm scale. The identified domain
architecture involves a plethora of ferroelectric domain boundaries and
junctions, including primary and secondary domain walls in both electrically
neutral and charged configurations, and topological line defects transforming
neutral secondary walls into two oppositely charged ones.
