Open Questions in CMR Manganites, Relevance of Clustered States, and Analogies with other Compounds

TL;DR

This paper discusses the current understanding and unknowns in manganites, emphasizing the significance of inhomogeneous clustered states and their potential relevance to other complex materials, proposing a new paradigm in condensed matter physics.

Contribution

It highlights the recent discovery of inhomogeneous states in manganites and explores their implications, suggesting these clustered states are a widespread phenomenon across various materials.

Findings

Inhomogeneous states are closely linked to colossal magnetoresistance.

Clustered states are more common than previously thought.

Potential for colossal-like effects in non-ferromagnetic compounds.

Abstract

This is an informal paper that contains a list of ``things we know'' and ``things we do not know'' in manganites. It is adapted from the conclusions chapter of a recent book by the author, {\it Nanoscale Phase Separation and Colossal Magnetoresistance. The Physics of Manganites and Related Compounds}, Springer-Verlag, Berlin, November 2002. The main new result of recent manganite investigations is the discovery of tendencies toward inhomogeneous states, both in experiments and in simulations of models. The colossal magnetoresistance effect appears to be closely linked to these mixed-phase tendencies, although considerably more work is needed to fully confirm these ideas. The paper also includes information on cuprates, diluted magnetic semiconductors, relaxor ferroelectrics, cobaltites, and organic and heavy fermion superconductors. These materials potentially share some common phenomenology with the manganites, such as a temperature scale $T^*$ above the ordering temperature where anomalous behavior starts. Many of these materials also present low-temperature phase competition. The possibility of colossal-like effects in compounds that do not involve ferromagnets is briefly discussed. Overall, it is concluded that inhomogeneous ``clustered'' states should be considered a new paradigm in condensed matter physics, since their presence appears to be far more common than previously anticipated.