  A wide variety of experimental results and theoretical investigations in
recent years have convincingly demonstrated that several transition metal
oxides and other materials, have dominant states that are not spatially
homogeneous. This occurs in cases in which several physical interactions --
spin, charge, lattice, and/or orbital -- are simultaneously active. This
phenomenon causes interesting effects, such as colossal magnetoresistance, and
it also appears crucial to understand the high temperature superconductors. The
spontaneous emergence of electronic nanometer-scale structures in transition
metal oxides, and the existence of many competing states, are properties often
associated with complex matter where nonlinearities dominate, such as soft
materials and biological systems. This electronic complexity could have
potential consequences for applications of correlated electronic materials,
because not only charge (semiconducting electronic), or charge and spin
(spintronics) are of relevance, but in addition the lattice and orbital degrees
of freedom are active, leading to giant responses to small perturbations.
Moreover, several metallic and insulating phases compete, increasing the
potential for novel behavior.
