Magneto-thermoelectric characterization of a HfTe5 micro-ribbon

Abstract

HfTe5 is a promising low-temperature thermoelectric material. Its thermoelectric power output has been investigated at different temperatures and with different dopants. Recently, research has focused on the nontrivial topological band structure of HfTe5. Whereas band structure simulations and angle-resolved photoemission spectroscopy experiments put HfTe5 at the transition between a weak and a strong topological insulator, observations of the chiral magnetic effect indicate that HfTe5 is instead a Dirac semimetal. In this study, we contribute to the investigation of transport phenomena in HfTe5 by magnetoresistance (MR) and magnetothermopower (MS) measurements on a single-crystalline HfTe5 microribbon measuring 20 μm × 2.1 μm × 0.7 μm, with a magnetic field applied perpendicular to the transport direction. Interestingly, we see an almost complete suppression of the thermopower for elevated magnetic fields at temperatures of T ≤ 100 K, while an increased magnetothermopower is observed for increasing magnetic fields at T ≥ 150 K. First, we analyze the magnetic field-dependence of the magnetoresistance and magnetothermopower for different temperatures and propose several possible transport mechanisms responsible for the vanishing magnetothermoelectric transport at low temperatures. Furthermore, we report on an increase in the thermoelectric power factor by up to 40% due to an applied magnetic field and for temperatures between 150 K and 300 K, which is the temperature range relevant for thermoelectric applications of HfTe5.