Point-contact spectroscopy on the La-doped Kondo insulator Ce3Bi4Pt3

Break-junction experiments have been carried out on the Kondo insulator (Ce 1-xLax)(3)Bi4Pt3 At T = 1.5 K and for x = 0, dV/dI versus V curves for poin t contacts with R-o less than or equal to 12 k Omega exhibit semiconducting behavior, i.e. decreasing dV/dI with increasing V. The finite dV/dI at V = 0 results from a finite density of states inside the band gap. For the La- doped compounds the semiconducting behavior is less pronounced and a step-l ike gap structure occurs at V approximate to +/- E-g/e. With increasing La concentration the step is shifted to lower V in qualitative agreement with resistivity data. The results suggest that La doping has two effects: reduc tion of the gap and introduction of impurity states in the band gap of Ce3B i4Pt3 (C) 1999 Elsevier Science B.V. All rights reserved.