Theoretical seminar | 01 December 2021

Axions are hypothetical particles that were originally postulated to resolve strong CP problem in quantum chromodynamics and are currently considered as promising dark matter candidates in astrophysics. While the search for cosmic axions is ongoing, some condensed matter systems give rise to the so-called emergent axions. Specifically, electrodynamics of such materials called axion topological insulators is captured by the equations of axion electrodynamics. Recently, axion topological insulators were realized in condensed matter systems. In this educational talk, I will discuss how topology is related to axion electrodynamics in these materials, what is the difference between the first and second Chern number and how nonzero magneto-electric coupling can arise in centrosymmetric materials.

Main paper/arXiv, related to the seminar, and other references

D.M. Nenno, et al. Nature Reviews Physics 2, 682-696 (2020)