Colossal Effects in Transition Metal Oxides Caused by Intrinsic Inhomogeneities

TLDR

The study draws an analogy to the Griffiths temperature for systems with two competing orders, suggesting that such inhomogeneities can produce a strong susceptibility to external fields, a behavior also seen in underdoped cuprates. The authors investigate how quenched disorder affects the competition between ordered states across a first‑order transition. They introduce a characteristic temperature scale, $T^{*}$, that governs the formation of ordered clusters. Classical models yield a phase diagram with quantum‑critical‑like features, revealing a low‑temperature paramagnetic regime of randomly oriented coexisting clusters that, when applied to manganites, explains colossal magnetoresistance.

Abstract

The influence of quenched disorder on the competition between ordered states separated by a first-order transition is investigated. A phase diagram with features resembling quantum-critical behavior is observed, even using classical models. The low-temperature paramagnetic regime consists of coexisting ordered clusters, with randomly oriented order parameters. Extended to manganites, this state is argued to have a colossal magnetoresistance effect. A scale ${T}^{*}$ for cluster formation is discussed. This is the analog of the Griffiths temperature, but for the case of two competing orders, producing a strong susceptibility to external fields. Cuprates may have similar features, compatible with the large proximity effect of the very underdoped regime.