Spin filtering in germanium/silicon core/shell nanowires with pseudo-helical gap

TL;DR

This paper demonstrates spin filtering in germanium/silicon core/shell nanowires via a pseudo-helical gap, achieved without magnetic fields, using ferromagnetic contacts and electrical tuning to control spin transport.

Contribution

It introduces a method to realize spin filtering in semiconductor nanowires through a pseudo-helical gap without magnetic fields, utilizing ferromagnetic contacts and gate tuning.

Findings

Observation of a hysteresis loop indicating spin filtering

Electrical control of the helical gap via gate voltage

Verification of polarized spin transport outside the gap

Abstract

Semiconductors with strong spin-orbit interactions can exhibit a helical gap with spin-momentum locking opened by a magnetic field. Such a gap is highly spin selective as a result of a topologically protected spin-momentum locking, which can be used for spin filtering. We experimentally demonstrate such a spin filtering effect in a quasi-ballistic p-type germanium/silicon core/shell nanowire (NW), which possesses a pseudo-helical gap without the application of magnetic field. Polarized hole spin injection to the NW is achieved using cobalt ferromagnetic contacts with controlled natural surface oxide on the NW as a tunnel barrier. Local and nonlocal spin valve effects are measured as the verification of polarized spin transport in the NW outside the helical gap. We electrically tune the NW into the helical gap by scanning its chemical potential with a gate. A hysteresis loop with three resistance states is observed in the local spin valve geometry, as an evidence of spin filtering in the helical gap.