Relevance of the pseudogap for the thermopower of CeNiSn

CeNiSn has been classified as a correlated semimetal with a low charge carrier concentration. The opening of an anisotropic pseudogap below 10 K has been confirmed from various experimental probes. The gap formation can be suppressed significantly by application of magnetic fields of 10 T along the easy a axis. We performed thermopower and Nernst effect measurements on high-purity single crystals of CeNiSn in the temperature range between 1.5 K and 200 K and in magnetic fields up to 7 T. Special care has been taken to correct the thermopower S for contributions from transverse components in a magnetic field. Our data clearly demonstrate the relevance of the pseudogap for the low-T thermopower. S(T) exhibits a large negative minimum below the temperature, at which the gap opens. Upon increasing magnetic field the minimum shifts to lower T whereas the absolute values at the minimum increase. We apply a simple model to describe this unusual field dependence of the thermopower