Generation of an anomalous linearly dispersing spin-polarized band in Bi-based topological insulators

TL;DR

This study reports the creation of a novel, spin-polarized, linearly dispersing electronic state in Bi-based topological insulator thin films, induced by ion bombardment and annealing, with unique spin and energy characteristics.

Contribution

The paper introduces an anomalous spin-polarized band (ALS) in Bi-based TIs, distinct from the regular TSS, generated through a specific surface treatment process.

Findings

The ALS spans up to ~650 meV at the Γ-point.

The ALS exhibits opposite spin-momentum locking compared to the TSS.

The Fermi velocity of ALS matches that of the TSS.

Abstract

We report the generation of an anomalous linearly dispersing, spin-polarized band in Bi-based topological insulator (TI) thin films, induced by soft Ar-ion bombardment followed by annealing. This extra band -- which we call the anomalous linearly dispersing state (ALS) -- is superimposed on the regular band structure including the topological surface state (TSS), spans an unusually large energetic range of up to ${\sim}\,\SI{650}{\milli\electronvolt}$ at the $\Gamma$-point, and appears near the Fermi energy. Spin-resolved measurements indicate spin-momentum locking with a helicity \emph{opposite} to that of the regular TSS. The Fermi velocity of the ALS, $v_\mathrm{F} = (5.1\pm 0.4)\times 10^{5}\,\frac m s$, is indistinguishable from that of the regular TSS, $(5.3\pm 0.5)\times 10^{5}\,\frac m s$. The observation is reproducible across samples of varying thickness and was confirmed at two independent synchrotron radiation facilities. We discuss different mechanisms for the physical origin of the observed ALS including sputtering-induced TSS relocation, bi-layer formation by,e.g., chalcogen removal, and high-index surface relocation.