Fermi level dependent spin pumping from a magnetic insulator into a topological insulator

Abstract

Topological spintronics aims to exploit the spin-momentum locking in the helical surface states of topological insulators for spin-orbit torque devices. We address a fundamental question that still remains unresolved in this context: does the topological surface state alone produce the largest values of spin-charge conversion efficiency or can the strongly spin-orbit coupled bulk states also contribute significantly? By studying the Fermi level dependence of spin pumping in topological insulator/ferrimagnetic insulator bilayers, we show that the spin Hall conductivity is constant when the Fermi level is tuned across the bulk band gap, consistent with a full bulk band calculation. The results suggest a new perspective, wherein "bulk-surface correspondence" allows spin-charge conversion to be simultaneously viewed either as coming from the full bulk band, or from spinmomentum locking of the surface state. :1906.11116v1 [cond-mat.mtrl-sci] arXiv

All‐Electrical Magnon Transport Experiments in Magnetically Ordered Insulators

“…In addition, topological insulators with their spinpolarized edge state provide novel functionalities in charge-tospin current conversion processes. [225,[233][234][235] Developing new MOIs to unlock new areas of magnon transport is another important aspect for material-oriented research. One of the major challenges is to establish MOIs with long magnon spin lifetimes to facilitate experiments on lengthscales accessible via nanolithography processes.…”

Large Damping Enhancement in Dirac‐Semimetal–Ferromagnetic‐Metal Layered Structures Caused by Topological Surface States

“…In other words, the sputtered α‐Sn thin films in this work represent an important model system for understanding material topology beyond single crystals. 6)The presented damping and spin mixing conductance enhancement induced by TSS in TDS α‐Sn films is as significant as that induced by TSS in TI materials. [ 9–13 ] This result, together with efficient magnetization switching induced by TSS in TDS α‐Sn films, [ 28 ] evidently show that TDS α‐Sn may be as promising as TI materials in terms of spintronic applications.…”

“…As such, the spin‐pumping effects are usually weak if the nonmagnetic layer is a metallic thin film with weak SOC, such as Cu and Ag, but can be very strong if the nonmagnetic layer is a heavy metal thin film with strong SOC, such as Pt and W. [ 5–8 ] The effects can be even stronger if the nonmagnetic component is a topological insulator (TI), such as Bi 2 Se 3 and SmB 6 ; [ 9–13 ] topological surface states in a TI exhibit intrinsic spin‐momentum locking, which is an extreme example of strong SOC. [ 14 ]…”

Voltage-control of damping constant in magnetic-insulator/topological-insulator bilayers

“…An essential feature of the FI/TI bilayer is that the TI bulk behaves as a semiconductor, enabling the control of the surface carrier density by a voltage. 35 Also, magnetically doped TI exhibit VCMA. 12,36 Hence, TIs are a promising candidate to achieve the voltagecontrol of magnetic damping.…”