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Spin-momentum locking provides a basic concept to control electron’s spin and charge flow in variety of material systems such as topological insulators, semiconductors, and heavy metals. Induced helical spin texture at the Fermi surface allows us to efficiently generate and detect spin polarization without an external magnetic field or magnetic materials. While spin generation and spin detection using spin-momentum locking have been intensively explored at Rashba interfaces and topological surface states, spin manipulation has yet to be demonstrated: it remains the missing ingredient towards full set of spin control by spin-momentum locking. Here, we experimentally manifested spin manipulation by spin-momentum locking in a magnetic focusing device [1]. We employ an InGaAs/InGaAsP heterostructure which shows strong SO-induced effective magnetic field. Such a large SO field generates and detects in-plane spin-polarized electrons by combining with lateral quantum point contacts (QPCs). By employing the lateral magnetic focusing device, weak out-of-plane external magnetic field focuses ballistic electrons from emitter to collector QPC by Lorentz force. Two QPCs allow us to polarize and detect electron spin along in-plane orientation due to strong SO interaction. We observed the enhanced focusing signal in collector QPC under spin polarized magnetic focusing regime. This indicates that the spin orientation in focused electrons have taken the opposite direction from that of the emitted spins. Electron spin rotates in a circular orbital motion while spin orientation is locked towards the SO field due to the spin-momentum locking. The findings of this study highlight the significance of the electron trajectory in controlling the spin phase through spin-momentum locking. The ability to control the spin phase by the orbital motion opens the door to the development of new concept on spintronic devices as well as topological electronics.
[1] M. Kohda et al., Scientific Reports in press (2019).
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