Anomalous Melting Transition of Charge-Ordered State in Manganites

Melting of charge-ordered state in (La,Ca)MnO sub 3 and (Pr,Ca)MnO sub 3 is characterized by an anomalously large decrease of the wave vector as much as 25% through the transition. High resolution lattice images obtained from electron microscopy reveal that the large change occurs as a result of formation of new clusters with charge-ordering modulation wavelength increased by integral lattice parameter. This is distinctly different from the typical melting transition such as charge density waves and our findings can be attributed to the discrete nature of the charge ordering on the manganese sites.