Thermoelectric transport in Weyl semimetal BaMnSb2: A first-principles study

Topological materials are often associated with exceptional thermoelectric properties. Orthorhombic $\mathrm{Ba}\mathrm{Mn}{\mathrm{Sb}}_2$ is a topological semimetal consisting of alternating layers of Ba, Sb, and MnSb. A recent experiment demonstrates that $\mathrm{Ba}\mathrm{Mn}{\mathrm{Sb}}_2$ has a low thermal conductivity and modest thermopower, promising as a thermoelectric material. Through first-principles calculations with Coulomb repulsion and spin-orbit coupling included, we studied the electronic structure, phononic structure, and thermoelectric transport properties of $\mathrm{Ba}\mathrm{Mn}{\mathrm{Sb}}_2$ in depth. We find that $\mathrm{Ba}\mathrm{Mn}{\mathrm{Sb}}_2$ exhibits a low lattice thermal conductivity, owing to the scattering of the acoustic phonons with low-frequency optical modes. Using the linearized Boltzmann transport theory with a constant relaxation time approximation, the thermopower is further calculated and an intriguing goniopolar transport behavior, which is associated with both $n$-type and $p$-type conduction along separate transport directions simultaneously, is observed. We propose that the figure of merit can be enhanced via doping in which electrical conductivity is increased while the thermopower remains undiminished. $\mathrm{Ba}\mathrm{Mn}{\mathrm{Sb}}_2$ is a potential platform for elucidating complex band structure effects and topological phenomena, paving the way to explore rich physics in low-dimensional systems.