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On the matter of topological insulators as magnetoelectrics
by N. P. Armitage, Liang Wu
N. Peter Armitage
||Armitage, N. Peter
||Exp. & Theor.
||Condensed Matter Physics - Experiment
It has been proposed that topological insulators can be best characterized
not as surface conductors, but as bulk magnetoelectrics that -- under the right
conditions-- have a universal quantized magnetoelectric response coefficient
$e^2/2h$. However, it is not clear to what extent these conditions are
achievable in real materials that can have disorder, finite chemical potential,
residual dissipation, and even inversion symmetry. This has led to some
confusion and misconceptions. The primary goal of this work is to illustrate
exactly under what real life scenarios and in what context topological
insulators can be described as magnetoelectrics. We explore analogies of the 3D
magnetoelectric response to electric polarization in 1D in detail, the formal
vs. effective polarization and magnetoelectric susceptibility, the 1/2
quantized surface quantum Hall effect, the multivalued nature of the
magnetoelectric susceptibility, the role of inversion symmetry, the effects of
dissipation, and the necessity for finite frequency measurements. We present
these issues from the perspective of experimentalists who have struggled to
take the beautiful theoretical ideas and to try to measure their (sometimes
subtle) physical consequences in messy real material systems.
Ontology / Topics
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Author comments upon resubmission
We have replied to all the comments and critiques of the referees and hope that you and they will now find the manuscript suitable for SciPost.
List of changes
- In this revised version we have added some additional discussion on the significance of the effect we found. Moreover near the end of the manuscript we have added some text on how the isolated 1⁄2 quantized response can be measured directly.
- We have added text explaining what experiments we believe still need to be done.
- We now say so explicitly that no experiment has measured an isolated single surface.
- We have changed Im to Re for Eq. 11
- We cite additional papers that the referee has pointed out on the fact that one cannot create Wannier functions that are localized and strictly respect the symmetry?
- We have added discussion on the important paper of Pesin and MacDonald.
- We have also now added a table at the end of the manuscript that makes a comparison between 1D polarization and the 3D ME effect.