Abstract
One of the most striking properties of three-dimensional topological insulators (TIs) is spin-momentum locking, where the spin is locked at right angles to momentum and hence an unpolarized charge current creates a net spin polarization. Alternatively, if a net spin is injected into the TI surface state system, it is distinctively associated with a unique carrier momentum and hence should generate a charge accumulation, as in the so-called inverse Edelstein effect. Here using a Fe/Al2O3/BN tunnel barrier, we demonstrate both effects in a single device in Bi2Te3: the electrical detection of the spin accumulation generated by an unpolarized current flowing through the surface states, and that of the charge accumulation generated by spins injected into the surface state system. This work is the first to utilize BN as part of a hybrid tunnel barrier on TI, where we observed a high spin polarization of 93% for the TI surfaces states. The reverse spin-to-charge measurement is an independent confirmation that spin and momentum are locked in the surface states of TI, and offers additional avenues for spin manipulation. It further demonstrates the robustness and versatility of electrical access to the spin system within TI surface states, an important step towards its utilization in TI-based spintronics devices.
Highlights
A bulk topological insulator (TI) is a new quantum phase of matter characterized by an insulating bulk, and gapless surface states that are occupied by massless Dirac fermions which exhibit many intriguing properties[1,2,3,4,5]
Epitaxial graphene/SiC(0001) are used as substrates, and Bi and Te fluxes are supplied by Knudsen cells held at 460 and 250 °C, respectively
The fact that spin is locked at right angles to momentum dictates that, given a momentum, i.e., electron motion or charge current, a spontaneous spin polarization should arise
Summary
A bulk topological insulator (TI) is a new quantum phase of matter characterized by an insulating bulk, and gapless surface states that are occupied by massless Dirac fermions which exhibit many intriguing properties[1,2,3,4,5]. We inject spin polarized electrons from the Fe into the Bi2Te3 surface state system, and electrically measure the charge accumulation in the direction orthogonal to that of the injected spin orientation. This provides independent confirmation that spin and momentum are locked in the Dirac surface states of TIs, and more importantly demonstrates versatile electrical access to the TI surface state spin system with important implications for the development of TI-based spintronic devices
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