Impurity-induced localization of quasiparticles in the presence of a pseudogap in CeNiSn

The effect of doping in CeNiSn has been studied by the measurements of electrical resistivity, Hall coefficient and magnetic susceptibility for single crystals of ${\mathrm{CeNi}}_{1\ensuremath{-}x}{T}_{x}\mathrm{Sn}$ $(T=\mathrm{Co},$ Cu, and Pt) and ${\mathrm{Ce}}_{1\ensuremath{-}y}{\mathrm{La}}_{y}\mathrm{NiSn}$ $(x,y=0.01$ and 0.05). All these impurities are found to increase the residual resistivity by several times up to 1 m\ensuremath{\Omega} cm for x or $y=0.01,$ while for x or $y=0.05$ the resistivities along the orthorhombic b and c axes saturate to values smaller than those for 0.01. Furthermore, the low-temperature increase in the Hall mobility of CeNiSn was found to be strongly suppressed in a similar way by all the impurities. These results indicate that residual carriers in CeNiSn with an anisotropic gap are immobilized by any impurity substituted either in the $4f$ site or the non-$4f$ site.