Band Structure of Topological Insulator BiSbTe1.25Se1.75

H Lohani,D Topwal,P Mishra,K Majhi,R Ganesan,P S Anil Kumar,B R Sekhar,U Manju,A Banerjee

doi:10.1038/s41598-017-04985-y

Abstract

We present our angle resolved photoelectron spectroscopy (ARPES) and density functional theory results on quaternary topological insulator (TI) BiSbTe1.25Se1.75 (BSTS) confirming the non-trivial topology of the surface state bands (SSBs) in this compound. We find that the SSBs, which are are sensitive to the atomic composition of the terminating surface have a partial 3D character. Our detailed study of the band bending (BB) effects shows that in BSTS the Dirac point (DP) shifts by more than two times compared to that in Bi2Se3 to reach the saturation. The stronger BB in BSTS could be due to the difference in screening of the surface charges. From momentum density curves (MDCs) of the ARPES data we obtained an energy dispersion relation showing the warping strength of the Fermi surface in BSTS to be intermediate between those found in Bi2Se3 and Bi2Te3 and also to be tunable by controlling the ratio of chalcogen/pnictogen atoms. Our experiments also reveal that the nature of the BB effects are highly sensitive to the exposure of the fresh surface to various gas species. These findings have important implications in the tuning of DP in TIs for technological applications.

Highlights

Discovery of the new quantum state of matter called topological insulators (TI) has attracted world wide interest due to their exotic properties which are manifestations of a non-trivial band topology[1, 2]
While most of the reported studies were focussed on the tunability by chemical doping or adding layers of other elements on the surface of TIs, the drifting of the topological surface state bands (SSBs) and Dirac point (DP) with aging of the surface which are important for device applications[21], has not been addressed adequately in this family of TIs9, 10
We present a detailed study of the electronic structure and aging effects of BiSbTe1.25Se1.75(BSTS) using angle resolved photoelectron spectroscopy (ARPES) in conjunction with density functional theory (DFT) based calculations

Summary

OPEN Band Structure of Topological

We present our angle resolved photoelectron spectroscopy (ARPES) and density functional theory results on quaternary topological insulator (TI) BiSbTe1.25Se1.75 (BSTS) confirming the non-trivial topology of the surface state bands (SSBs) in this compound. The resistivity can be optimized in the Sb doped quaternary alloy Bi2−xSbxTe3−ySey by changing the ratio of the pnictogen (Bi and Sb) and chalcogen (Se and Te) atoms without disturbing its crystallinity In this compound, topological nature with different bulk resistivity has been experimentally observed in a wide range of x and y combinations[14]. The ARPES data, we observe topological character of the SSBs and a warping of the Fermi surface (FS) These results are consistent with our calculated SSBs which fall within the region of bulk band gap of BSTS. Experiments performed with constant dosing of different gases show that the BB effects are highly sensitive to the gas species

Results and Discussion

Methods

Author Contributions

Additional Information