Experimental verification of band convergence in Sr/Na doped PbTe

Band convergence is one of the most successful guidelines for the synthesis of high-performance thermoelectric materials. However, its experimental verification is missing. We believe that the solid understanding of the electronic structure will lead to an efficient synthesis of high performance thermoelectric materials, but the electronic structure of almost all of the thermoelectric materials is not studied in detail. In this study, quantum oscillations and scanning tunneling microscopy STM dI/dV measurements are performed to reveal the band structure of Sr/Na-doped PbTe [1], which was reported to exhibit zT=2.5 in the previous study [2]. The STM dI/dV measurements show that the energy difference between the L band and \Sigma band decreases with Sr/Na doping, leading to the band convergence. Also, the band gap of pristine PbTe (~200 meV) increases by Sr/Na doping (~350 meV). The STM dI/dV measurements can reveal electronic structure including the unoccupied band, which is not accessible by angle-resolved photoemission spectroscopy (ARPES). We believe that STM dI/dV measurements provide a bird's-eye view for the development of thermoelectric materials.

[1] Y. Hattori, S. Yoshizawa, K. Sagisaka, Y. Tokumoto, K. Edagawa, T. Konoike, S. Uji, and T. Terashima, Phys. Rev. B 108, 125119 (2023).

[2] G. Tan, F. Shi, S. Hao, L.-D. Zhao, H. Chi, X. Zhang, C. Uher, C. Wolverton, V. P. Dravid, and M. G. Kanatzidis, Nat. Commun. 7, 12167 (2016).