TY - JOUR
T1 - Microscopic investigation of Bi2-xSbxTe3-ySey systems
T2 - On the origin of a robust intrinsic topological insulator
AU - Nam, Hyoungdo
AU - Xu, Yang
AU - Miotkowski, Ireneusz
AU - Tian, Jifa
AU - Chen, Yong P.
AU - Liu, Chang
AU - Hasan, M. Zahid
AU - Zhu, Wenguang
AU - Fiete, Gregory A.
AU - Shih, Chih Kang
N1 - Publisher Copyright:
© 2017
PY - 2019/5
Y1 - 2019/5
N2 - 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.
AB - 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.
KW - Aging effect
KW - BeTeSe
KW - BiSbTeSe
KW - Dirac point
KW - Topological insulator
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U2 - 10.1016/j.jpcs.2017.10.026
DO - 10.1016/j.jpcs.2017.10.026
M3 - Article
AN - SCOPUS:85032342812
SN - 0022-3697
VL - 128
SP - 251
EP - 257
JO - Journal of Physics and Chemistry of Solids
JF - Journal of Physics and Chemistry of Solids
ER -