Microscopic investigation of Bi2-xSbxTe3-ySey systems: On the origin of a robust intrinsic topological insulator

Hyoungdo Nam, Yang Xu, Ireneusz Miotkowski, Jifa Tian, Yong P. Chen, Chang Liu, M. Zahid Hasan, Wenguang Zhu, Gregory A. Fiete, Chih Kang Shih

Research output: Contribution to journalArticle

4 Scopus citations

Abstract

One of the most important challenges in the field of topological insulators (TI) is to find materials with nontrivial topological surface state (TSS) while keeping the bulk intrinsic (insulating). In this letter, we report microscopic investigations of BiSbTeSe2 (1112) and Bi2Te2Se (221) alloys which have been proposed as candidates to achieve an intrinsic bulk. Scanning tunneling microscopy (STM) confirms previous macroscopic experiments that 221 is an ordered alloy with a Te-Bi-Se-Bi-Te sequence. Nevertheless, it also reveals that the ordering is not perfect with the surface chalcogen layer containing 85% Te and 15% Se. On the other hand, STM shows that 1112 is a random alloy with a fine mixture of (Bi, Sb) in the pnictogen layers and (Te, Se) in the top/bottom chalcogen layers. A freshly cleaved 221 sample surface shows an intrinsic bulk with the Fermi energy, EF, in the gap, but quickly becomes n-type with aging, similar to the aging effect reported by others [27,32]. By contrast, the random alloy 1112 show remarkable robustness against aging and the EF remains within the gap even after aging for 7 days. We attribute this result to the nanoscale fine mixture of the random alloy which provides an effective doping compensation in very fine length scale, thus enabling its bulk to remain intrinsic against aging.

Original languageEnglish (US)
Pages (from-to)251-257
Number of pages7
JournalJournal of Physics and Chemistry of Solids
Volume128
DOIs
StatePublished - May 2019

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

Keywords

  • Aging effect
  • BeTeSe
  • BiSbTeSe
  • Dirac point
  • Topological insulator

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