  The quest to understand correlated electronic systems has pushed the
frontiers of experimental measurements toward the development of new
experimental techniques and methodologies. Here we use a novel home-built
uniaxial-strain device integrated into our variable temperature scanning
tunneling microscope that enables us to controllably manipulate in-plane
uniaxial strain in samples and probe their electronic response at the atomic
scale. Using scanning tunneling microscopy with spin-polarization techniques,
we visualize antiferromagnetic domains and their atomic structure in Fe1+yTe
samples, the parent compound of iron-based superconductors, and demonstrate how
these domains respond to applied uniaxial strain. We observe the bidirectional
antiferromagnetic domains in the unstrained sample, with an average domain size
of 50 to 150 nm, to transition into a single unidirectional domain under
applied uniaxial strain. The findings presented here open a new direction to
utilize a valuable tuning parameter in scanning tunneling microscopy, as well
as other spectroscopic techniques, both for tuning the electronic properties as
for inducing symmetry breaking in quantum material systems.
