  Owing to the unusual geometry of kagome lattices-lattices made of
corner-sharing triangles-their electrons are useful for studying the physics of
frustrated, correlated and topological quantum electronic states. In the
presence of strong spin-orbit coupling, the magnetic and electronic structures
of kagome lattices are further entangled, which can lead to hitherto unknown
spin-orbit phenomena. Here we use a combination of vector-magnetic-field
capability and scanning tunnelling microscopy to elucidate the spin-orbit
nature of the kagome ferromagnet Fe3Sn2 and explore the associated exotic
correlated phenomena. We discover that a many-body electronic state from the
kagome lattice couples strongly to the vector field with three-dimensional
anisotropy, exhibiting a magnetization-driven giant nematic
(two-fold-symmetric) energy shift. Probing the fermionic quasi-particle
interference reveals consistent spontaneous nematicity-a clear indication of
electron correlation-and vector magnetization is capable of altering this
state, thus controlling the many-body electronic symmetry. These spin-driven
giant electronic responses go well beyond Zeeman physics and point to the
realization of an underlying correlated magnetic topological phase. The
tunability of this kagome magnet reveals a strong interplay between an
externally applied field, electronic excitations and nematicity, providing new
ways of controlling spin-orbit properties and exploring emergent phenomena in
topological or quantum materials.
