Spin-textured Volkov–Pankratov states and their tunnel magnetoresistance response

Abstract

Volkov-Pankratov (VP) states are a family of sub-gap states that appear at the smooth interface/domain wall between topologically distinct gapped states. We carry out quantum transport simulations on a 2D lattice model to demonstrate the emergence of such states in the edge spectrum of a quantum spin Hall system subjected to a smoothly varying exchange field that switches its sign at a given spatial point. We show the VP states possess non-trivial spin textures that can be characterized by a winding number in real space. It is further demonstrated that the application of an electric field along the edge provides control of this spin texture without altering the winding number. Finally, we illuminate how these spin textures can be read off via the local tunnel magnetoresistance (TMR) response of spin-polarized tunnel probes attached to the edge and the TMR can be controlled by purely electrical means akin to a Datta-Das type spin transistor.