Fig. 6. DOS evolution and carrier concentration versus disorder diagram.

(A) On the basis of the shape of DOS (see fig. S8), N(E) is shaped qualitatively as downward parabolas. Disorder herein will cause exponential tails. In Fe₇Se₈ (left), E_F cuts in the middle of the band; electrons stay itinerant near the E_F. The doping of Li does not only slightly raise E_F but also introduces disorder and leads to the appearance of a mobility edge E_M, which separates localized areas (shaded region) and itinerant area part. When the E_M shifts below E_F (middle), MIT occurs. At higher lithium contents (right), VRH will become more prominent with the enhancement of disorder as described in the text. (B) This figure is adapted from Gantmakher and Man (44). Horizontal axis represents disorder strength (W), vertical axis represents carrier concentration (n), and solid lines represent the boundaries of MIT (explained by Anderson localization or Mott transition mechanism). Asterisks and dots represent Li_xFe₇Se₈, GeSb₂Te₄, and metal alloy.