Enhancement of the thermoelectric figure of merit in the Dirac semimetal Cd3As2 by band-structure and -filling control

Abstract

Topological materials attract a considerable research interest because of their characteristic band structure giving rise to various new phenomena in quantum physics. Besides this, they are tempting from a functional materials point of view: Topological materials bear potential for an enhanced thermoelectric efficiency because they possess the required ingredients, such as intermediate carrier concentrations, large mobilities, heavy elements etc. Against this background, this work reports an enhanced thermoelectric performance of the topological Dirac semimetal Cd₃As₂ upon alloying the trivial semiconductor Zn₃As₂. This allows to gain fine-tuned control over both the band filling and the band topology in Cd_3-x Zn _x As₂. As a result, the thermoelectric figure of merit exceeds 0.5 around $x=0.6$ and $x=1.2$ at elevated temperatures. The former is due to an enhancement of the power factor, while the latter is a consequence of a strong suppression of the thermal conductivity. In addition, in terms of first-principle band structure calculations, the thermopower in this system is theoretically evaluated, which suggests that the topological aspects of the band structure change when traversing $x=1.2$ .

Keywords: Cd3As2; Dirac semimetal; Thermoelectric materials; band filling; band structure engineering; figure of merit.