Tunneling Tuned Spin Modulations in Ultrathin Topological Insulator Films

TL;DR

This study investigates how quantum tunneling affects spin polarization in ultrathin topological insulator films, revealing tunable spin properties crucial for future spintronic devices.

Contribution

It provides experimental and theoretical insights into the relationship between tunneling and spin polarization in topological insulator films, enabling spin control in nano-devices.

Findings

Spin polarization is high away from the Brillouin zone center.

Polarization decreases with tunneling in thin insulating films.

Polarization saturates faster in thicker metallic films.

Abstract

Quantitative understanding of the relationship between quantum tunneling and Fermi surface spin polarization is key to device design using topological insulator surface states. By using spin-resolved photoemission spectroscopy with p-polarized light in topological insulator Bi2Se3 thin films across the metal-to-insulator transition, we observe that for a given film thickness, the spin polarization is large for momenta far from the center of the surface Brillouin zone. In addition, the polarization decreases significantly with enhanced tunneling realized systematically in thin insulating films, whereas magnitude of the polarization saturates to the bulk limit faster at larger wavevectors in thicker metallic films. Our theoretical model calculations capture this delicate relationship between quantum tunneling and Fermi surface spin polarization. Our results suggest that the polarization current can be tuned to zero in thin insulating films forming the basis for a future spin-switch nano-device.