Spin-Polarized Quantum Well States on Bi$_{2-x}$Fe$_x$Se$_3$

TL;DR

This study uses low temperature STM to image and analyze spin-polarized quantum well states and topological surface states in doped Bi$_{2-x}$Fe$_x$Se$_3$, revealing their coexistence, spin polarization, and potential for spintronics.

Contribution

It demonstrates the coexistence of quantum well states with topological surface states in doped Bi$_{2-x}$Fe$_x$Se$_3$ and characterizes their spin polarization and robustness.

Findings

Quantum well states coexist with topological surface states.

Both states remain spin-polarized and protected from backscattering.

Breakdown of linear dispersion due to hexagonal warping observed.

Abstract

Low temperature scanning tunneling microscopy is used to image the doped topological insulator Bi$_{2-x}$Fe$_x$Se$_3$. Interstitial Fe defects allow the detection of quasiparticle interference (QPI), and the reconstruction of the empty state band structure. Quantitative comparison between measured data and density functional theory calculations reveals the unexpected coexistence of quantum well states (QWS) with topological surface states (TSS) on the atomically clean surface of Bi$_{2-x}$Fe$_x$Se$_3$. Spectroscopic measurements quantify the breakdown of linear dispersion due to hexagonal warping. Nonetheless, both QWS and TSS remain spin-polarized and protected from backscattering to almost 1 eV above the Dirac point, suggesting their utility for spin-based applications.