Thursday, December 13, 2012

The puzzle of linear magnetoresistance in topological insulators

Tony Wright brought to my attention a nice (brief) review paper on the arXiv
Magnetotransport and induced superconductivity in Bi based three-dimensional topological insulators
M. Veldhorst, M. Snelder, M. Hoek, C. G. Molenaar, D. P. Leusink, A. A. Golubov, H. Hilgenkamp, A. Brinkman
[published version is here].

In passing, I note there is a brief section on Shubnikov de Haas oscillations and the Berry phase. A more extensive discussion can be found in a recent preprint by Tony Wright and I.

Here I briefly discuss the very nice section about linear magnetoresistance (LMR) (i.e. a magnetoresistance that increases linearly with magnetic field, in contrast to the quadratic increase characteristic of regular metals) that have been observed in Bi-based topological insulators. This was of particular interest to me because I previously posted about the puzzle of linear magnetoresistance in Ag2Te [which may or may not be a topological insulator]. Similar issues and theoretical models arise here.

The physical origin of the observed magnetoresistance is also not clear.

First, it is hard to distinguish the contributions from the bulk and the surface conductivity. But, the authors suggest "it seems unlikely that the LMR ... originates from the surface states alone".

Second, the authors raise questions about whether the materials are really in the lowest Landau level, as assumed in Abrikosov's quantum magnetoresistance model. They then critically examine a model by Wang and Lei that requires a linear dispersion and a small Zeeman splitting. This can be distinguished from Abrikosov's model via the density dependence of the LMR.

Two more theoretical models are then discussed.

So, the challenge is to come up with definitive experiments to rule out some of the theories.

I thank Xiaolin Wang for interesting me in this problem last year. His experimental results are reported in this PRL and APL.

No comments:

Post a Comment