X-ray spectroscopy of the metal-insulator transition in Yb1-xGdxTe and Yb1-xLaxTe

We report extended X-ray absorption fine structure (EXAFS) of Yb1-xGdxTe an d Yb1-xLaxTe, two solid solutions which show an insulator-metal transition (IMT) as a function of x for a high donor concentration x(c) approximate to 0.2. The results are correlated to transport experiments and X-ray diffrac tion data, to analyse the IMT in relation to the structure at both a local and a macroscopic scale. A bimodal distribution is found for rare earth-Te nearest distances in these compounds crystallized in the fee structure. In particular, we find the less rigid Yb-Te bond can be used as a local probe for the wavefunction of the electrons introduced by La or Gd donors, hence a new insight on the metal-insulator transitions which are of a different n ature in the two solid solutions.