Giant Thermopower Changes Related to the Resistivity Maximum and Colossal Magnetoresistance in EuCd$_2$P$_2$

We present the thermopower of EuCd$_2$P$_2$, a material which exhibits a large resistivity peak with significant magnetic field dependence in the temperature range of 10–25 K. In the same region, we observe a highly unusual behavior of the thermopower with two sign changes and giant extrema. The overall variation of the thermopower exceeds 4000 μV=K and takes place in an extremely narrow temperature region of less than 5 K. The anomaly is suppressed completely in a small magnetic field of 0.5 T. We discuss this observation using a simple drift-diffusion picture and taking into account that the temperature gradient inducing the thermopower voltage is accompanied by a gradient of the electrical resistivity. Our simple estimation yields the correct magnitude, shape, and field dependence of the thermopower anomaly observed in EuCd$_2$P$_2$. These results open a new route to giant thermopower values via gradients of electronic properties.