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Skyrmion crystal as a promising thermoelectric converter: A prediction from first-principles

Date : Tuesday, August 29th, 2017 14:00 - 15:00 Place : Seminar Room 5 (A615), 6th Floor, ISSP Lecturer : Mr. Yo Pierre Mizuta Affiliation : Graduate School of Natural Science and Technology, Kanazawa University Committee Chair : OZAKI Taisuke (ext.63285)
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.


[1] M. Ikhlas et al., Nature Physics (2017) doi:10.1038/nphys4181.
[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).

(Published on: Wednesday August 9th, 2017)