Tuning valley degeneracy with band inversion

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 10; no. 3
• Main Authors: Toriyama, Michael Y., Brod, Madison K., Gomes, Lídia C., Bipasha, Ferdaushi A., Assaf, Badih A., Ertekin, Elif, Snyder, G. Jeffrey
• Format: Journal Article
• Language: English
• Published: United States Royal Society of Chemistry 16.12.2021
• Subjects: INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
• ISSN: 2050-7488; 2050-7496

Valley degeneracy is a key feature of the electronic structure that benefits the thermoelectric performance of a material. Despite recent studies which claim that high valley degeneracy can be achieved with inverted bands, our analysis of rock-salt IV–VI compounds using first-principles calculations and k•p perturbation theory demonstrates that mere band inversion is an insufficient condition for high valley degeneracy; rather, there is a critical degree to which the bands must be inverted to induce multiple carrier pockets. The so-called “band inversion parameter” is formalized as a chemically-tunable property, offering a design route to achieving high valley degeneracy in compounds with inverted bands. In conclusion, we predict that the valley degeneracy of rock-salt IV–VI compounds can be increased from NV = 4 to NV = 24, which could result in a corresponding increase in the thermoelectric figure of merit zT.