paper

The interplay between double exchange, super-exchange, and Lifshitz localization in doped manganites

arXiv:cond-mat/0111244 · doi:10.1103/PhysRevB.66.104430

Abstract

Considering the disorder caused in manganites by the substitution of Mn by Fe or Ga, we accomplish a systematic study of doped manganites begun in previous papers. To this end, a disordered model is formulated and solved using the Variational Mean Field technique. The subtle interplay between double exchange, super-exchange, and disorder causes similar effects on the dependence of T_C on the percentage of Mn substitution in the cases considered. Yet, in La $_{2/3}$ Ca $_{1/3}$ Mn $_{1 - y}$ Ga $_{y}$ O $_{3}$ our results suggest a quantum critical point (QCP) for $y \approx 0.1 - 0.2$ , associated to the localization of the electronic states of the conduction band. In the case of La $_{x}$ Ca $_{x}$ Mn $_{1 - y}$ Fe $_{y}$ O $_{3}$ (with $x = 1/3, 3/8$ ) no such QCP is expected.

6 pages + 3 postscript figures. Largely extended discussion