Non-Local Spin Transport in Topological Insulator Nanowires

The momentum and spin of charge carriers in Topological Insulators(TI) are constrained to be perpendicular due to spin-orbit coupling. Sb₂Te₃ is a TI materials with a bulk band gap of 0.28 eV and surface states consisting of a single Dirac cone in the band gap. Single crystalline Sb₂Te₃ nanowires were synthesised. E-beam lithography were used to pattern two outer Au leads and two magnetic tunnel junction(MTJ) inner leads on individual Sb₂Te₃ nanowires. The MTJ leads consist of a free Py (Ni₈₀Fe₂₀) layer, whose magnetization determines the magnitude and direction of spin current injected into nanowire.
The two-point resistance between Au contacts under magnetic field sweep showed positive magneto-resistance, originating from weak anti-localization of carriers in nanowire induced by spin-orbit interaction, serves as evidence of a strong impact of spin orbit interaction in nanowires.
The symmetry of non-local spin valve (NLSV) signal is dramatically different from that of a NLSV with a channel that lacks spin-momentum locking(SML) (e.g. graphene). Two parallel states of the injector and detector magnetic moments give rise to different NLSV voltage values, which is never observed in conventional NLSVs. This unusual symmetry is a signature of SML in Sb₂Te₃ nanowire surface state.