Skyrmion crystal as a promising thermoelectric converter: A prediction from first-principles
e-mail: t-ozaki@issp.u-tokyo.ac.jp
The anomalous Nernst effect (ANE), a heat-to-electric conversion in mutually transverse directions, can be driven by an emergent magnetic field B originating from inhomogeneous magnetic moments in solids. Large ANE has been experimentally confirmed in various ferromagnets, and only very recently, also in an antiferromagnet [1]. Here we theoretically propose that, the Skyrmion crystal (SkX), in which magnetic topological objects Skyrmions are crystallized, is another candidate to host large ANE.
We have found through first-principles calculations on a single s-orbital model using the package OpenMX [2] and Wannier90 [3] that, in a two dimensional SkX phase a large ANE would appear when chemical potential μ is properly tuned (Figure) [4]. This was interpreted as due to its characteristic distribution of Chern numbers among the bands (each Chern number representing quantized flux of B field through each electronic band in momentum space).
Following such an observation in the simplest model of square SkX [4], our subsequent computations on a more realistic oxide film also predict large ANE.
This motivates further studies of ANE in the SkX family, in quest of better thermoelectric materials that exploit this effect.
[2] T. Ozaki et al., Open source package for Material eXplorer, http://www.openmx-square.org/
[3] A. A. Mostofi et al., http://www.wannier.org.
[4] Y. P. Mizuta and F. Ishii, Scientific Reports 6, 28076 (2016).