  Topological insulators host topology-linked boundary states, whose spin and
charge degrees of freedom could be exploited to design topological devices with
enhanced functionality. We experimentally observe that dissipationless chiral
edge states in a spin-orbit coupled anomalous Floquet topological phase exhibit
topological spin texture on boundaries, realized via a two-dimensional quantum
walk. Our experiment shows that, for a walker traveling around a closed loop
along the boundary in real space, its spin evolves and winds through a great
circle on the Bloch sphere, which implies that edge-spin texture has nontrivial
winding. This winding is linked to the bulk Dirac Hamiltonian around the
energy-gap opening point. Our experiment confirms that two-dimensional
anomalous Floquet topological systems exhibit topological spin texture on the
boundary, which could inspire novel topology-based spintronic phenomena and
devices.
