Probing charge/orbital correlation in La1.2Sr1.8Mn2O7 by Raman spectroscopy

Raman spectra have been investigated for a single crystal of La 1.2 Sr 1.8 Mn 2 O 7 that shows colossal magnetoresistance around the Curie temperature T C = 126 K. Several broad phonon peaks grow with decrease of temperature down to T C but disappear below T C , which can be clearly ascribed to a change in the charge/orbital correlation by comparison with the spectra for the charge/orbital ordered states of the layered manganites (La 0.5 Sr 1.5 MnO 4 and LaSr 2 Mn 2 O 7 ). Such a real-space charge density fluctuation is also observed to cause the low-energy diffuse Raman response, the B 1g component of which is critically suppressed below T C as well.