Thermoelectric Transport in Topological Crystalline Insulator and Topological Semimetal Nanowires

Many of the topological materials (e.g. Bi₂Te₃ and Sb₂Te₃) are also well-known thermoelectric materials with high figures of merit ZTs. This ‘coincidence’ is not accidental but is because the two groups of materials share some similar properties, i.e. they are composed of heavy elements and have small bulk band gaps. Theoretical calculations have suggested the possibility of enhancing thermoelectric properties by utilizing topological non-trivial states. In this talk, I will present our recent experimental studies of thermoelectric transport in some representative topological materials, including SnTe-based topological crystalline insulators (TCIs) and iridium oxide-based topological semimetals (TSMs). Grown by chemical vapor deposition, the TCIs and TSMs are (quasi-)one-dimensional nanowires with large surface-area-to-volume ratios and well-defined facets. Measurements of the Seebeck coefficient, and electrical and thermal conductivities were performed on the same individual nanowires as a function of temperature, allowing for accurate determination of their ZTs. I will discuss the enhancement of Seebeck coefficient and suppression of thermal conductivity in connection with the topological states, doping, alloying, and nanostructuring.