Abstract
The metal-insulator transition, and the associated magnetic transition, in the colossal magnetoresistance
CMR regime of the one-orbital model for manganites is studied here using Monte Carlo MC techniques in
two-dimensional clusters. Both cooperative oxygen lattice distortions and a finite superexchange coupling
among the t2g spins are included in our investigations. Charge and spin correlations are studied. In the CMR
regime, a strong competition between the ferromagnetic metallic and the antiferromagnetic charge-ordered
insulating states is observed. This competition is shown to be important to understand the resistivity peak that
appears near the critical temperature. Moreover, it is argued that the system is dynamically inhomogeneous
with short-range charge and spin correlations that slowly evolve with MC time, producing the glassy characteristics
of the CMR state. The local density of states LDOS is also investigated and a pseudogap PG,
identified as a dip in the LDOS at the Fermi energy, is found to exist in the CMR temperature range. The width
of the PG in the LDOS is calculated and directly compared to recent scanning-tunneling-spectroscopy STS
experimental results. The observed agreement between our calculation and the experiment suggests that the
depletion of the conductance at low bias observed experimentally is a reflection on the existence of a PG in the
LDOS spectra. The apparent homogeneity observed via STS techniques could be caused by the slow time
characteristics of this probe. Faster experimental methods should unveil a rather inhomogeneous state in the
CMR regime, as already observed in neutron-scattering experiments.
