Negative longitudinal magnetothermopower in the topological semimetal ZrTe5

The chiral anomaly is one of the unusual effects of Weyl fermions and has attracted much interest. Experimental observation of this effect has largely been focused on a negative longitudinal magnetoresistance, which, however, has been proven to be insufficient. Thermoelectric experiment, a technique complimentary to the electrical resistivity and able to the capability to reveal the energy dependence of electron transport, has not been reported in many relevant semimetals. Here, we study the electrical and thermoelectric properties of a topological semimetal, ZrTe5. Besides a previously reported negative magnetoresistance (NMR), a negative magnetothermopower (MTEP) is observed when the magnetic field is parallel to the temperature gradient. Both the magnetoconductivity and MTEP follow a quadratic dependence on the magnetic field. Moreover, the quadratic coefficient of MTEP is about twice as large as that of magnetoconductivity. These observations are consistent with the effect of the chiral anomaly. We also discuss other possible origins of these observations, such as current jetting, ionized impurity scattering, and spin-related effects.