Topological matter and localisation effects 

Topological materials demonstrate novel states of matter that can emerge due to symmetry breaking. An example class of materials is called as topological insulators in which the bulk is characterised by gapped energy bands leading to electronically insulating behaviour whilst the surface is comprised of a gapless state leading to metal like behaviour [1][2]. In addition to this, the unique spin dynamics of these topological insulators make them useful for future applications in spintronics. 

Weak anti-localisation behaviour in charge conductivity is an effect that often arises in strong spin orbit coupling materials, e.g., topological materials. A phenomenon where certain electron scattering paths are supressed due to the topological surface states with peculiar spin texture leads to a measurable decrease in the electronic resistance. This effect can be used to probe the specific carrier dynamics within the novel surface states. However, it should be noted that this effect could occur in the bulk as well with different mechanisms [3][4]. Separating out these signals in thin film topological insulators is challenging but can provide insight into the unique dynamics in charge transport of the materials.

Bi_2-xSb_xTe₃ and Bi₂Se₃ are such examples of this family of topological insulators. Recently, we successfully demonstrated that the carrier type of Bi_2-xSb_xTe₃ was adjusted between electrons and holes by controlling Sb concentration. Thus, this material presents an opportunity to study the effect of carrier type and carrier concentration on the weak anti-localisation. This can then be contrasted with similar studies on Bi₂Se₃.

 

 

[1] A. Bansil, H. Lin, and T. Das, “Colloquium: Topological band theory,” Rev. Mod. Phys. 88, 021004, 2016.

[2] T. Arakane, T. Sato, S. Souma, K. Kosaka, K. Nakayama, M. Komatsu, T. Takahashi, Z. Ren, K. Segawa, Y. Ando, “Tunable Dirac cone in the topological insulator Bi_2-xSb_xTe_3-ySe_y,” Nature Commun. 3, 636, 2012.

[3] L. Bao, L. He, N. Meyer, X. Kou, P. Zhang, Z.-G. Chen, A. Fedorov, J. Zou, T. Riedemann, T. Lograsso, K. Wang, G. Tuttle, and F. Xiu, “Weak antilocalization and quantum oscillations of surface states in topological insulator Bi₂Se₂Te,” Scientific Reports 2, 726, 2012.

[4] K. Eto, Z. Ren, A. A. Taskin, K. Segawa, and Y. Ando, “Angular-dependent oscillations of the magnetoresistance in Bi₂Se₃ due to the three-dimensional bulk fermi surface,” Phys. Rev. B 81, 195309, 2010.