Topological Insulator Sb2Te3 Research Articles

Spiral growth of topological insulator Sb2Te3 nanoplates

Sb2Te3 nanoplates synthesized by vapor phase deposition method have been systemically investigated employing atomic force microscopy, which exhibit regular spiral structures on the surface. The height of spiral steps is determined to be 1 nm corresponding to one quintuple layer, with an inter-step separation ranging from 500 nm to 1 μm. Growth mechanism of spiral structures on the Sb2Te3 nanoplate surface is elucidated, which can be applied to other layered materials with van der Waals epitaxy growth. The electrostatic properties of Sb2Te3 nanoplates with spiral structures are also simultaneously characterized.

Probing two topological surface bands of Sb2Te3by spin-polarized photoemission spectroscopy

Using high resolution spin- and angle-resolved photoemission spectroscopy, we map the electronic structure and spin texture of the surface states of the topological insulator Sb2Te3. In combination with density functional calculations (DFT), we directly show that Sb2Te3 exhibits a partially occupied, single spin-Dirac cone around the Fermi energy, which is topologically protected. DFT obtains a spin polarization of the occupied Dirac cone states of 80-90%, which is in reasonable agreement with the experimental data after careful background subtraction. Furthermore, we observe a strongly spin-orbit split surface band at lower energy. This state is found at 0.8eV below the Fermi level at the gamma-point, disperses upwards, and disappears at about 0.4eV below the Fermi level into two different bulk bands. Along the gamma-K direction, the band is located within a spin-orbit gap. According to an argument given by Pendry and Gurman in 1975, such a gap must contain a surface state, if it is located away from the high symmetry points of the Brillouin zone. Thus, the novel spin-split state is protected by symmetry, too.

Single Dirac cone on the Cs-covered topological insulator surface Sb2Te3(0001)

Using angle-resolved photoelectron spectroscopy we investigate the surface electronic structure of the three-dimensional topological insulator (TI) Sb2Te3(0001). Our data show the presence of a topological surface state in the bulk energy gap with the Dirac-point located above the Fermi level. The adsorption of Cs-atoms on Sb2Te3(0001) gives rise to a downward energy shift of the electronic valence band states which saturates at a value of ~200 meV. For the saturation coverage the Dirac-point of the linearly dispersive surface state resides in close proximity to the Fermi level. The electronic structure of the Cs/Sb2Te3 interface therefore considerably deviates from previously studied metal-TI interfaces based on the isostructural compound Bi2Se3 which points to the importance of atomic composition in these hetero systems.

Anomalous thermal expansion of Sb2Te3 topological insulator

We have investigated the temperature dependence of the linear thermal expansion along the hexagonal c axis (ΔL), in-plane resistivity (ρ), and specific heat (Cp) of the topological insulator Sb2Te3 single crystal. ΔL exhibits a clear anomaly in the temperature region 204–236 K. The coefficient of linear thermal expansion α decreases rapidly above 204 K, passes through a deep minimum at around 225 K, and then increases abruptly in the region 225–236 K. α is negative in the interval 221–228 K. The temperature dependence of both α and Cp can be described well by the Debye model from 2 to 290 K, excluding the region around the anomaly in α.

Atomically smooth ultrathin films of topological insulator Sb2Te3

The growth and characterization of single-crystalline thin films of topological insulators (TIs) is an important step towards their possible applications. Using in situ scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES), we show that moderately thick Sb2Te3 films grown layer-by-layer by molecular beam epitaxy (MBE) on Si(111) are atomically smooth, single-crystalline, and intrinsically insulating. Furthermore, these films were found to exhibit a robust TI electronic structure with their Fermi energy lying within the energy gap of the bulk that intersects only the Dirac cone of the surface states. Depositing Cs in situ moves the Fermi energy of the Sb2Te3 films without changing the electronic band structure, as predicted by theory. We found that the TI behavior is preserved in Sb2Te3 films down to five quintuple layers (QLs).

First-principles studies of the three-dimensional strong topological insulators Bi2Te3, Bi2Se3 and Sb2Te3

Bi2Se3, Bi2Te3 and Sb2Te3 compounds have recently been predicted to be three-dimensional (3D) strong topological insulators. In this paper, based on ab initio calculations, we study in detail the topological nature and the surface states of this family of compounds. The penetration depth and the spin-resolved Fermi surfaces of the surface states are analyzed. We also present a procedure from which a highly accurate effective Hamiltonian can be constructed based on projected atomic Wannier functions (which keep the symmetries of the systems). Such a Hamiltonian can be used to study the semi-infinite systems or slab-type supercells efficiently. Finally, we discuss the 3D topological phase transition in the Sb2(Te1−xSex)3 alloy system.