Thermoelectrics: from Longitudinal to Transverse

In this article, we show fundamentals and recent advances on the transverse thermoelectric generation, in which a thermopower is generated in the direction perpendicular to an applied temperature gradient. Transverse thermoelectric generation is one of the central topics in condensed matter physics, and can be a breakthrough approach to solve long-standing technological problems with contact resistances in thermoelectric generators. We review here the six currently known driving mechanisms: the ordinary Nernst effect, the anomalous Nernst effect, goniopolar materials, the spin Seebeck effect, Seebeck-driven transverse thermoelectric generation, and ($p \times n$)-type multilayers. This article summarizes the principles and functionalities of these transverse thermoelectric effects and discusses their potential as "Future energy".