Magnetoelectric effects on a topological insulator surface

TKM Institutsseminar

Speaker:

Stefan Rex

Date:

23/02/2017 14:00

Where:

Raum 10.01, Geb. 30.23 (Physikhochhaus), Campus Süd

Affiliation:

Norwegian University of Science and Technology Trondheim, Norway

Host:

PD Dr. I. Gornyi

Abstract

When a gap is induced in the Dirac surface states of a topological insulator (TI),
e.g. by proximity to a ferromagnetic layer, a topological magnetoelectric effect
(TME) arises, whereby applying an electric field locally induces a magnetic
polarization. In this talk, I will demonstrate that the physics behind the TME
can also lead to different phenomena.

I will first discuss how the TME is modified in the presence of Coulomb interaction
among the Dirac fermions. I will show that these long-range interactions lead to a
nonlocal contribution to the TME, which can also be expressed as a topological magnetic
dipolar interaction.

In the second part, I will consider the interface of a TI with a bipartite magnet.
I will show that, for suitable parameters, the magnetic response of the system to
an electric field can turn into a staggered field rather than a net magnetization.
Thus, the overall effect can vary significantly depending on the microscopic properties
of the magnet.