The role of spin in thermoelectricity

Thermoelectric (TE) materials and devices are crucial for renewable thermal-to-electrical energy conversion applications. The optimization of TE performance can be achieved by manipulating four fundamental degrees of freedom: charge, lattice, spin and orbital. Historically, most strategies to improve TE performance focus on phonon and electron charge transport properties. However, in the past 15 years, the field of spin caloritronics, which explores the interplay among heat, charge and spin, has emerged. The inclusion of spins has introduced conceptually innovative mechanisms and versatile functionalities for solid-state thermal-to-electrical energy conversion. Here, we review the recent theoretical and experimental progress in the field of spin caloritronics. We discuss the strategic role of spin-related mechanisms in improving charge-based TE performance and the recent developments in the novel magneto-TE and thermospin effects as well as their potential applications. This Review offers a perspective for understanding the role of spin in TE, designing new high-efficiency TE materials and developing new TE technology beyond the conventional framework.