Axion Electrodynamics of Topological Materials
22nd May 2017, PHYSIKALISCHES KOLLOQUIUM, HNB, Ruhr-Universität Bochum
Start: 22nd May 2017 12:00
End: 22nd May 2017 01:30 p.m.
Flavio Nogueira, Ruhr-Universität Bochum
K. Efetov, Ruhr-Universität Bochum
The electromagnetic response of topological states of matter typically features a so called axion term in the effective Lagrangian. This term is a topologically invariant and leads to new physically interesting effects in topological insulators, superconductors, and Weyl semimetals. In this talk we will discuss the physical consequences of the axion electrodynamics in heterostructures involving topological insulators, ferromagnets, and type II superconductors. One interesting specific example that will be discussed is the one of a topological insulator vertical Josephson junction. Due to the axion term a magnetic field applied perpendicular to the junction makes the vortex lines become the source of electric fields, leading in this way to a vortex - driven ac Josephson effect. This yields an example where the vortices become charged, carrying a fractional charge. This effect is a kin of the so called Witten effect, which predicts that in an axionic system magnetic monopoles acquire a fractional electric charge. This Josephson - Witten effect open s possibilities to electrically manipulate vortices via topological currents, which can in turn be used to create new devices. We briefly discuss the prospects of using these charged vortices as anyons and the possibility of braiding them for quantum computation.