Condensed Matter and AMO Seminar

Condensed Matter and AMO Seminar

Topology in Magnets



November 20, 2019 - 3:00pm to 4:00pm


Howey School of Physics




University of Toronto


Electrons in solids have been shown to support new non-interacting topological phases of matter such as topological insulators and semimetals. In this talk I will discuss three aspects of how topology plays a role in magnetic solids, which intrinsically involve strong electronic correlations. We will begin with a discussion of simple magnetically ordered states, and show how momentum space topology plays an important role in understanding fluctuations around such ordered states.

I will illustrate this via the emergence of Dirac magnons and associated edge states in a new cobaltate material we have studied in collaboration with neutron scattering experimentalists, and also discuss related work from other groups. Turning to more complex magnetic orders, we find that real space topology plays a key role in understanding the physics of skyrmions, tiny magnetic swirls which are of great interest in the context of dense information storage. I will discuss how this real space topology gets imprinted onto electronic states, leading to various types of unconventional responses such as quantum oscillations and measured anomalous optical Kerr effects.

Such responses can be used to probe or potentially manipulate skyrmions. Similar to soft-matter systems, skyrmions can exist as isolated particles, form thermally fluctuating liquids, or assemble into crystals. Starting from the crystalline state of skyrmions, we show that if quantum fluctuations become very strong, such crystals can undergo T=0 melting into an exotic chiral quantum liquid. This spin liquid state is found to exhibit unusual many-body topological properties, bearing a striking resemblance to the fractional quantum Hall state of matter.