  The superposition of flexoelectronic doping and topological phonons give rise
to topological electronic magnetism of phonon in an inhomogeneously strained Si
in the bilayer structure with metal. In case of ferromagnetic metal and Si
bilayer structure, the flexoelectronic doping will also give rise to larger
spin current, which will lead to large spin to charge conversion due to
topological electronic magnetism of phonon. By applying a temperature
difference to ferromagnetic metal/Si bilayer structure under an applied strain
gradient, a large thermoelectric response can be generated. In this
experimental study, we report a large spin dependent thermoelectric response at
Ni80Fe20/Si bilayer structure. The spin dependent response is found to be an
order of magnitude larger than that in Pt thin films and similar to topological
insulators surface states in spite of negligible intrinsic spin-orbit coupling
of Si. This large response is attributed to the flexoelectronic doping and
topological electronic magnetism of phonons, which was uncovered using
topological Nernst effect measurement. This alternative and novel approach of
using inhomogeneous strain engineering to address both spin current density and
spin to charge conversion can open a new window to the realization of
spintronics and spin-caloritronics devices using metal and doped-semiconductor
layered materials.
