#### Condensed Matter Seminar - Shuichi Murakami, Tokyo Institute of Technology - " Topological magnon transport in ferromagnets"

Magnons (spin waves) are low-energy excitations in magnets. We theoretically study effects caused by Berry curvature due to magnon band structure in ferromagnetic insulators, in analogy with anomalous Hall and spin Hall effect for electrons. From the semiclassical theory, the Berry curvature causes thermal Hall effect for magnons, and we calculate its thermal Hall conductivity. The same result is reproduced by linear response theory. We demonstrate this for the (classical) magnetostatic waves due to dipolar interaction in ferromagnets such as YIG. Furthermore, we also discuss the "gapped" variant of this effect in magnonic crystals. In the magnonic crystals, spatial periodicity opens a magnonic gap in the band structure. By formulating the gauge field and Chern number, we demonstrate that in some magnonic crystals which are periodic structures of two different ferromagnetic materials, the Chern numbers become nonzero, causing topological chiral edge modes similar to the quantum Hall effect.

**Location:**
Jadwin A09

**Date/Time: **10/16/12
at
3:00 pm
- 10/16/12
at
4:30 pm

**Category: **Condensed Matter Seminar

**Department: **Physics