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Three-dimensional topological insulator feature of ternary chalcogenide Ge2Bi2Te5

Shangjie Tian, Yuchong Zhang, Chenhao Liang, Yuqing Cao, Wenxin Lv, Xingyu Lv, Zhijun Wang, Tian Qian, Hechang Lei, Shouguo Wang

Abstract

The exploration of novel topological insulators (TIs) beyond binary chalcogenides has been accelerated in pursuit of exotic quantum states and device applications. Here, the layered ternary chalcogenide Ge2Bi2Te5 is identified as a three-dimensional TI. The bulk electronic structure of Ge2Bi2Te5 features a hole-type Fermi surface at Fermi level EF, which dominates the transport properties. Moreover, an unoccupied topological surface state with a Dirac point located at 290 meV above EF has been observed. Theoretical calculations confirm a bulk bandgap and a nontrivial Z2 topological invariant (000;1). The present study demonstrates that the material family of layered tetradymite-like ternary compounds is an important platform to explore exotic topological phenomena.

Three-dimensional topological insulator feature of ternary chalcogenide Ge2Bi2Te5

Abstract

The exploration of novel topological insulators (TIs) beyond binary chalcogenides has been accelerated in pursuit of exotic quantum states and device applications. Here, the layered ternary chalcogenide Ge2Bi2Te5 is identified as a three-dimensional TI. The bulk electronic structure of Ge2Bi2Te5 features a hole-type Fermi surface at Fermi level EF, which dominates the transport properties. Moreover, an unoccupied topological surface state with a Dirac point located at 290 meV above EF has been observed. Theoretical calculations confirm a bulk bandgap and a nontrivial Z2 topological invariant (000;1). The present study demonstrates that the material family of layered tetradymite-like ternary compounds is an important platform to explore exotic topological phenomena.
Paper Structure (4 figures)

This paper contains 4 figures.

Figures (4)

  • Figure 1: (a) Structure of Ge$_2$Bi$_2$Te$_5$ single crystal. The red, green and orange balls represent Ge, Bi and Te atoms, respectivety. (b) XRD pattern of a Ge$_2$Bi$_2$Te$_5$ single crystal. The inset shows the photograph of a typical Ge$_2$Bi$_2$Te$_5$ single crystal. (c) Powder XRD pattern and Rietveld fit of crushed Ge$_2$Bi$_2$Te$_5$ crystals.
  • Figure 2: (a) Temperature dependence of $\rho_{xx}(T)$ of Ge$_2$Bi$_2$Te$_5$ single crystal. (b) and (c) MR and Hall resistivity as a function of $\mu_{0}H$ between 2 K and 300 K. (d) Temperature dependences of $n_a(T)$ and $\mu (T)$ derived from the linear fits of $\rho_{yx}(\mu_{0}H)$ curves and zero-field $\rho_{xx}(T)$ data.
  • Figure 3: (a) and (b) Intensity plot of conventional ARPES data along $\bar{\Gamma}-\bar{\rm M}$ and $\bar{\Gamma}-\bar{\rm K}$ direction. Dashed lines (schematic) are guides to the eye indicating the dispersion of the bulk valence bands. (c) and (d) Intensity plot of pump-probe ARPES data along $\bar{\Gamma}-\bar{\rm M}$ and $\bar{\Gamma}-\bar{\rm K}$ direction. The dashed lines indicate the topological surface states. (e) Plots of the experimental constant energy contours (CECs) at different energy close to the Dirac point.
  • Figure 4: (a) Band structure of bulk Ge$_2$Bi$_2$Te$_5$ with spin-orbit coupling. (b) Surface state of the topmost Te--Bi--Te atomic trilayer at the Te-termination of Ge$_2$Bi$_2$Te$_5$.