Observation of Unconventional Quantum Spin Textures in Topological Insulators

TLDR

Topological insulators exhibit a rare quantum organization of electrons, and exotic spin‑transport phenomena such as the quantum spin Hall effect are thought to arise from topological order that requires spin‑sensitive measurements, which have been lacking. The authors employed Mott polarimetry to image spin textures, enabling the determination of topological quantum numbers from the measured spin degrees of freedom. The study reports the first observation of surface electrons carrying a topological Berry’s phase and definite spin chirality, revealing the origin of topological order and chiral properties in Sb and Bi₁₋ₓSbₓ via Mott polarimetry.

Abstract

A topologically ordered material is characterized by a rare quantum organization of electrons that evades the conventional spontaneously broken symmetry–based classification of condensed matter. Exotic spin-transport phenomena, such as the dissipationless quantum spin Hall effect, have been speculated to originate from a topological order whose identification requires a spin-sensitive measurement, which does not exist to this date in any system. Using Mott polarimetry, we probed the spin degrees of freedom and demonstrated that topological quantum numbers are completely determined from spin texture–imaging measurements. Applying this method to Sb and Bi 1–x Sb x , we identified the origin of its topological order and unusual chiral properties. These results taken together constitute the first observation of surface electrons collectively carrying a topological quantum Berry's phase and definite spin chirality, which are the key electronic properties component for realizing topological quantum computing bits with intrinsic spin Hall–like topological phenomena.