Reentrant Charge Ordering In Manganites as Experimental Evidence for a ``Strain Glass"

A reentrant charge-ordering transition occurs within the micron scale phase separated manganite (La,Pr)$_{5/8}$Ca$_{3/8}$MnO$_{3}$. This low temperature state, in which charge-ordered and ferromagnetic-metallic phases coexist, accompanies spin glass-like magnetism. Furthermore, thermal conductivity measurements reveal an irreversibility characteristic of a freezing transition in the lattice degrees of freedom, strongly suggesting the presence of inhomogeneous long-range strain. Our results point to a unique phase transition from a ``strain liquid'' to a ``strain glass'' state where phase-separated regions strongly interact via martensitic accommodation strain resulting in a cooperative freezing of the combined charge/spin/strain degrees of freedom.