Novel Method for “Power Generation by Utilizing Waste Heat”, a Theoretical Prediction

Researchers of Kanazawa University discovered, through computer simulation, the possibility of generation of enormous thermoelectric effect by skyrmion, a whirl-like structure, produced by the spins of electrons. This study suggests a novel method for developing energy saving technology. It is expected that research and development will be promoted for realization of enormous thermoelectric effect by exploring into more realistic materials such as metal oxides.

In the modern society, sustainable utilization of energy in environment-friendly manners is more and more important. Thermoelectric conversion is expected to play bigger roles, transforming abundant waste heat into electricity. Among such research and development for higher efficiency, utilized generally is the Seebeck effect, voltage induction in the longitudinal direction of the thermal/electrical flow induced by temperature gradient generated by supplying heat to a part of a sample of material. While a number of investigations have made contributions by somehow strengthening the Seebeck effect, a theoretical study was herein performed to suggest that thermoelectric conversion efficiency could be improved by utilizing the Nernst effect, voltage induction in the perpendicular direction of thermal/electrical flow induced by temperature gradient. 

The Nernst effect is observed by applying magnetic field in the perpendicular direction to the electric flow from outside. In this study, the research team paid attention to the anomalous Nernst effect, induced by magnetic field generated by the spins of electrons instead of applying magnetic field from outside. This magnetic field is induced as a quantum physics effect, whirl-like geometric structure of the spins of electrons being transferred into geometric structure of the electronic states. The research principle was to utilize this effect in the thermoelectric conversion. 

The research team performed a detailed simulation on a model skyrmion crystal, in which large anomalous Nernst effect had been expected based on previous studies. Thus, the magnitude of the anomalous Nernst effect was evaluated and the thermoelectric coefficients were calculated in consideration of the effect.

It was found that in the case of special Fermi level, enormous anomalous Nernst effect would be observed as a large thermoelectric coefficient. Furthermore, it was found that the larger the radius of individual skyrmions, the larger the thermoelectric coefficient. If this effect is well controlled, thermoelectric conversion with better efficiency than that with the Seebeck effect conventionally employed may be realized. The current study did not rely on experiment-based information but utilized computer simulation of electronic states only with solid structure and its components. With larger-scale utilization of a supercomputer, it should be possible to investigate similar effects of more complicated and realistic materials.

From viewpoints of applied sciences, the result of the current study indicates that designing thermoelectric materials of high quality should be possible by taking advantage of the relationship of skyrmion structure and large thermoelectric coefficient found herein.

In addition, the current study contributes to basic sciences by finding a peculiar phenomenon in quantum physics, that the geometric structure, skyrmion crystal formed by the spins of electrons, makes magnetic field reflecting more abstract geometric property of electronic states, which in turn gives rise to large anomalous Nernst effect.

The present article was published online in Scientific Reports, an online journal by Nature Publishing Group, on June 16, 2016.



Title: Large anomalous Nernst effect in a skyrmion crystal
Journal: Scientific Reports 6, article number: 28086 (2016)
Authors: Yo Pierre MIZUTA, and Fumiyuki ISHII
Doi: 10.1038/srep28076

Grants-in-Aid on Scientific Research 25790007, 25390008 and 15H01015 from JSPS, the MEXT HPCI Strategic Program, and Kanazawa University SAKIGAKE Project.