Comprehensive study of band structure driven thermoelectric response of ZrTe5

We report a transport, thermodynamic, and spectroscopic study of ZrTe5 with a focus on elucidating the connections between its band structure and unusual thermoelectric properties. Using time and angle resolved photoemission spectroscopy we observe a small electronic band gap and temperature dependent Fermi level which traverses from a single valence to conduction band with lowering temperature, consistent with previous reports. This low temperature Fermi surface closely matches that derived from quantum oscillations, suggesting it is reflective of the bulk electronic structure. The Seebeck and low field Nernst response is characterized by an unusually large and nonmonotonic temperature evolution. We find this can be quantitatively explained using a semiclassical model based on the observed band character and a linear temperature shifting of the Fermi level. Additionally, we observe a large, nonsaturating enhancement of both thermoelectric coefficients in magnetic field. We show this can be captured by the Zeeman energy associated with a large effective g factor of 25.8 consistent with that derived from Lifshitz-Kosevich analysis of the quantum oscillations. Together these observations provide a comprehensive picture of ZrTe5 as a model high mobility small Fermi surface system and potential platform for significant magnetic field driven thermoelectricity.