Bi2Te1.6S1.4 - a Topological Insulator in the Tetradymite Family

TL;DR

This paper reports the synthesis, structure, and electronic properties of Bi2Te1.6S1.4, a new topological insulator with unique surface states and increased ionic character due to sulfur incorporation.

Contribution

It introduces Bi2Te1.6S1.4 as a novel topological insulator with detailed structural and electronic characterization, highlighting its distinct surface states and ionic properties.

Findings

Presence of topological surface states with exposed Dirac point

High-quality crystal growth from melt

S-rich limit of the Bi-Te-S Tetradymite phase

Abstract

We describe the crystal growth, crystal structure, and basic electrical properties of Bi2Te1.6S1.4, which incorporates both S and Te in its Tetradymite quintuple layers in the motif -[Te0.8S0.2]-Bi-S-Bi-[Te0.8S0.2]-. This material differs from other Tetradymites studied as topological insulators due to the increased ionic character that arises from its significant S content. Bi2Te1.6S1.4 forms high quality crystals from the melt and is the S-rich limit of the ternary Bi-Te-S {\gamma}-Tetradymite phase at the melting point. The native material is n-type with a low resistivity; Sb substitution, with adjustment of the Te to S ratio, results in a crossover to p-type and resistive behavior at low temperatures. Angle resolved photoemission study shows that topological surface states are present, with the Dirac point more exposed than it is in Bi2Te3 and similar to that seen in Bi2Te2Se. Single crystal structure determination indicates that the S in the outer chalcogen layers is closer to the Bi than the Te, and therefore that the layers supporting the surface states are corrugated on the atomic scale.