$\pi$ Spin Berry Phase in a Quantum-Spin-Hall-Insulator-Based Interferometer: Evidence for the Helical Spin Texture of the Edge States

Abstract

Quantum spin Hall insulator is characterized by the helical edge states, with the spin polarization of electron being locked to its direction of motion. Although the edge-state conduction has been observed, unambiguous evidence of the helical spin texture is still lacking. Here, we investigate the coherent edge-state transport in an interference loop pinched by two point contacts. Due to the helical character, the forward inter-edge scattering enforces a $\pi$ spin rotation. Two successive processes can only produce a nontrivial $2\pi$ or trivial $0$ spin rotation, which can be controlled by the Rashba spin-orbit coupling. The nontrivial spin rotation results in a geometric $\pi$ Berry phase, which can be detected by a $\pi$ phase shift of the conductance oscillation relative to the trivial case. Our results provide a smoking gun evidence for the helical spin texture of the edge states. Moreover, it also provides the opportunity to all-electrically explore the trajectory-dependent spin Berry phase in condensed matter.

5 pages, 3 figures, version to be published in Phys. Rev. Lett

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• Spin field-effect transistor in a quantum spin-Hall device
• Spin Berry phase in a helical edge state: Sz nonconservation and transport signatures
• Spin-polarized voltage probes for helical edge state: a model study
• Random-gate-voltage induced Al'tshuler-Aronov-Spivak effect in topological edge states
• Transport theory for electrical detection of the spin texture and spin-momentum locking of topological surface states
• Volkov-Pankratov states on the edge of a quantum spin Hall system
• Robust Majorana bound state in pseudo-spin domain wall of 2-D topological insulator
• Manipulation of helical states revealed by crossed Andreev reflection