Topological phonons in an inhomogeneously strained silicon-4: Large spin dependent thermoelectric response and thermal spin transfer torque due to topological electronic magnetism of phonons

TL;DR

This paper demonstrates that inhomogeneous strain in silicon-metal bilayers induces topological phonons that generate large spin-dependent thermoelectric responses, advancing spintronics and spin-caloritronics applications.

Contribution

It reveals how flexoelectronic doping and topological phonons in strained silicon-metal bilayers produce significant spin-dependent thermoelectric effects, a novel approach in spintronics.

Findings

Large spin-dependent thermoelectric response in Ni80Fe20/Si bilayer.

Response magnitude comparable to topological insulators.

Attribution of effects to topological phonons and flexoelectronic doping.

Abstract

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.